You're not the first person to express that opinion, and there is a lot of merit to it in terms of basic party ideology.
Hikind has been in the Assembly for decades, so most likely has had many conversations about switching to the GOP, but has steadfastly remained where he is.
It's probably a matter of coming to the conclusion that his political goal is to stay in his current seat for life, or at least as long as he possibly can. There aren't any practical chances for him to move up to higher office politically because of demographics, and he is pretty well assured of re-election to the state assembly from his current district. He could possibly win that district as a Republican, but why take the chance on a plunge into the unknown, especially if the Pubbies seem to be destined to be in the minority in the Assembly forever? At present, I believe he may hold some committee chairmanship as a majority Democrat.
BTW, Hikind has not only endorsed Romney in this year's presidential election, but he has plans to work for him in Jewish communities in the battleground states of Pennsylvania and Florida.
Sounds like a DINO (Democrat In Name Only). And you’re right—there is probably a complex calculus behind is decision to stay D.