With all those callers in between you and villian, he's getting decent odds to call with lots of holdings. 22, 99, JT are all entirely possible.
But your flop bet seems pretty weak to me, it's less than 1/4 of the pot, and only .10 more than your pre-flop raise. That leaves you vulnerable both to draws and a bluff from someone who puts you on something like a missed AK.