you are giving a horrible price to draws and weak hands so your equity vs his continuing range is very poor compared to your equity against his continuing range if you bet half pot. you narrow his c/c range to just a few hands you beat while his c/r range will probably contain more draws yet still have you burned. this is not to say that your jacks arent very strong heading into the turn action but in way ahead/way behind situations your sizing simply must be smaller. yes there are two flush draws but when you are at the turn and the board is paired you must consider that you are wa/wb the vast majority of the time