Why are there so many short stackers at high/mid stakes cash games? Is it because they don't want to make deep decisions? It's annoying browsing the lobby and almost every table has like 4-5 short stacks.

Why don't they just go play SNGs and get off the cash table?

/end rant

I know this is a bit of rant on your part, but there is a serious answer to your question.

People play poker for lots of reasons. One reason is to look like a baller to their friends. So some people will play higher than their skill level would indicate. At first, they will buy a full stack. They lose a lot of money quickly. A student of the game would accept that they weren't ready to play that high and drop down. However with their self-identity on the line, they come up with the alternative of short stacking to be able to keep saying, "I'm a 100nl player." They still aren't winning, but they are losing less because their mistakes aren't as obvious.

Are they buying in for the level that is permitted for that given table? If so, what's your problem?

To make money from bad plays by opponents who are tilted by the existence of short stacks.

I don't like short stackers. It's ok if they don't like me too.

It can be mathematically advantageous if there are a couple of bigger stacks in the game, due to the larger stacks having a higher SPR which makes for trickier decisions. I think it's especially the case in PLO where playing 40bb deep allows you to make a commitment decision on the flop. Someone with 100bb might not want to make that commitment.

Basically this.

It's just a different strategy pre/post and in multiway spots can potentially give you an edge as you'll realize more equity generally speaking because you'll have the pot odds to call without worrying about turn/river bets. Your c-bets/shoves on flops can put other players in 3-way spots in wierd positions because of the SPR and position (monkey in the middle) kind of thing.

That is not the answer as to why many top PLO players, like, Ike Hatton, routinely buy in short.

Understanding the reasons will markedly improve a persons understanding of poker strategy.

#research

my question is whats up with all the broken stacks at the micros? i constantly see random sizes like 12BBs 20BBs and so on Plus when their stack takes a hit they dont top up they just keep playing until someone takes the rest of their stack. Its like they dont even know their is a way to add money to your stack.

Optimal stack size is ultimately a function of your opponents' skill levels and their stack sizes. If you are sitting at a table with two world class players, who are both 1000 bbs deep, and three fish, who are all playing 50 bb stacks, how much do you really want to buy in for? It is a question of risk vs reward. Of course we want to have a 50 bb stack, so we can stack any of the fish, but don't have to face agonizing deep stack turn and river decisions against extremely capable opponents.

Another reason to short stack is when you first sit down at a table, and don't know any of the players there. At this point you are blind. You might be at a horrible table, in which case being short protects you, because the absolute amount of money you can lose is significantly less. You can double this protect by starting off with a very nitty short stack strategy. Then you observe and study your opponents. Hopefully they will not be quite as interested in you as you are in them, and you can gain an information asymmetry to have an edge later on. You determine the different skill sets of your opponents, measure them for aggression, and determine how much you want to add on for if anything. You can always add on for more chips later, but you are not allowed to subtract chips from your stack. If it turns out there are several deep stack whales playing every hand, then you add on for the max, especially if conditions are good otherwise as well (no overly aggro players on your immediate left, for example, good fish to reg balance).

Also, a lot of fish short stack. So personally I'm on the lookout for tables with short stacks.

I'm a little confused about this statement. SPR is based on effective stack size, right? A 100bb stack vs. a 40bb stack is really just a 40bb stack effective. I.e., the 100bb stack is just as committed due to SPR as the 40bb stack if they're playing against each other.

Or am I misunderstanding what you're stating?

The reason is the same it’s always been: correctly playing a 20BB stack lets you exploit other players while being unexploitable. That’s why platforms banned shortstackers years ago.
You have to understand that playing a shorter stack is the correct approach for them because it limits their losses.
Yes, in a heads-up game. If you play 6max and 5 players have 100BB, they’ll play each other according to that. Now if the sixth guy has only 20BBs, he gets to play short stack strategy against those players.

Extremely easy and common example: Player A raises, player B 3bets. Now you have player C who can just shove in his 20BB stack and B is committed to call because of pot odds, even if he 3bet a hand that would fold to the regular 4bet of a 100BB stack.

If your stack size is 40 bb at a table where oppenents have a range of stack sizes, what is the maximum effective stack you could have in a hand?

If you have a stack size of 100 bb, what is the maximum effective stack size you could have?

As stated by others, a main reason is pot odds.

Suppose you know your hand has 25% to 30% equity on the river. Villain all-in bets 100 into a pot of 100.

Case A: Your stack is 100, You are getting pot odds of 2 to 1 so a call is -EV as you need equity of 33%

Case B: Your stack is 20. You are getting pot odds of (100+20)/20 = 6 to 1 so a call is highly +EV.

Now one big disadvantage of short stacking is you lose the opportunity to play turns and rivers most of the time. To some degree this can be an advantage, if you combine short stacking with nitty play, because tight players have an advantage pre and on the flop, whereas loose players have an advantage on the big streets. But because the pot is so much bigger on the turn and river, and equities are more stratified, there is massive opportunity for profit especially if you are against unskilled players.