The 8 hits much of "3 to a straight/3 to a flush" flop peel range. Given that its still 3 opponents bet for value IMO. I can think of four reasons they call you on the flop:
1.) They are peeling a rando backdoor draw Giving 54s/75s/97s/T9s a free card seems like the worst case scenario, plus they may try to turn a turned OESD into a bluff which would be great for you
2.) They are waiting to k/r a weaker King Bet and raise for two streets of value. If you can trap a caller in between even better
3.) They are hoping to bluff catch an A high The 8 doesn't really improve the bluffs in your range so bet to punish them for hero calling. Its harder for a low pair to go into hero call mode given that its 4 way pot, but it can still happen, especially given your read of BTN and SB
4.) They turn their hand into a bluff on the turnBet for more yum yum
Even if this was heads up on the turn I think I'd still bet. I imagine you only really induce a river bluff/thin value bet vs the type of player who would also be willing to turn their hand into a bluff on the turn.
