there is about 20k in the pot when you move in, he has to call a little over 10k, so he has 2-1.
If he loses he will have 10k still, with blinds of 600/1200 this is not great but he is still ok.
He raised 3 1/2 x BB. if he then folds after a raise like that, especially when he had 2-1, anyone who is watching closely will now try to run him over.
So, there are lots of reasons for him to call even though his hand is very beatable.
There are frequent raisers who can fold and frequent raisers who can't, you need to know which one he is before you make that move.
As a rule, you don't want to be lowering your starting hands to take on the aggressive guy.
My experience is that a flop steal would have been far more effective than a preflop steal with JT when he has 2-1 odds and has you covered.
..........or, you could always fold
