I don't think I've ever seen a good player cold 4-bet oop to 900 (with stacks like this in a spot like this) with a mid-pair (probably because it's fairly atrocious)---> shoving pre loses a lot of it's luster. These 4-bets are historically always AA, KK, AK or air. OP's read (omg lol live read) was that villain was on the lighter side (AK or air). In order to best exploit this lightness, OP chose to flat in position and then get it in (over the pending c-bet) on any reasonable flop. There are
a lot of reasonable flops for J
J
, OP just didn't get one. Variance.