First of all, if you feel your opponents are exploitable and they will not adjust to you exploiting them, then playing an exploitative approach will make more money than a strictly GTO approach. So use your exploits if you're confident in them.
A player loses EV vs a GTO opponent - that does not adjust to exploit them - by making pure strategy EV mistakes. In other words, performing an action that is the opposite of what a GTO opponent considers a "pure strategy" or 100% action. 72o is folded UTG 100% of the time, and therefore opening or limping with that hand would be a pure strategy EV mistake.
Let's say the board is A7233r in a sb vs btn 100bb 3bet pot where the GTO player is OOP and has bet every street and the opponent is IP now facing a river jam.
The IP player is indifferent to calling with certain hands as the GTO opponent has a "perfectly" balanced river range. For example, if the IP player has JJ, the EV of call and the EV of fold are both roughly 0 and therefore JJ is folded and called both at some frequency. However, AQ is a pure call (100% and no folds)and calling is very +EV with AQ. If IP were to fold AQ on the river, that would be a pure strategy mistake, and he would be "losing" that EV. Similarly, if IP were to call with a hand that is a pure fold (such as a hand that cannot beat some bluffs of the GTO player) this would be a -EV call and the GTO player would "gain" that EV.
This simple river spot logic can be applied to earlier streets as well but it gets a lot more complicated.
Another example of a pure strategy EV mistake is incorrect hand selection preflop. Certain hands perform better in terms of their playability and raw equity than other hands. In an extreme example imagine an opponent raising a range from CO that folds suited aces, but opens offsuit connectors and 1 gappers like 67o/57o. This will influence the EV of his range not only preflop directly (in terms of having to fold too much to 3bets) but it will also impact the EV of his range on future streets due to the raw equity of his range being lowered, as well as the playability of those individual hands in that range. While a GTO opponent will not adjust his play, the overall EV of the opponents range will still be lowered.
There was a short video by David Alford that had the A7233r hand example in it:
https://www.youtube.com/watch?v=4eKdtqFMZe8