They are seemingly considering this primarily because they are upset at PM Netanyahu over his backtracking on several promises, primarily the promise to pass the Draft Law in tandem with the budget. In addition to that they see an opportunity to attach themselves to the Gantz bandwagon, and they think they can help him form a government without Yair Lapid and the other more left-wing parties. Additionally, this would be relieved of partnering with the extremist Ben Gvir, they would be rid of Amir Ohana, the current Speaker of the Knesset who is openly homosexual and while they have lived with it until now they don't like it, and it would temper the anti-haredi sentiments around the country while at the same time achieving the budgets they want and need for the yeshivas and kollelim as opposition to their budget demands would almost disappear if they help Gantz form a government.

Personally I think this is bogus. Whether they should do this or not, I do not see it happening. I see them floating this possibility purely to pressure Netanyahu to cave on some of the issues he has been backtracking on. Unless the next government is Gantz, Likud and the Haredi parties, which isnt likely to happen, I dont see how they think they can help Gantz form a government with Gantz while leaving Lapid out. The numbers arent there. Even if Gantz gets the 30+ seats he is polling at, adding the 18 or so Haredi seats to that (between Shas and UTJ, assuming they all agree to this), still leaves them far short of 61, and they need Lapid or some other parties to complete that. Smotritch and Ben Gvir wont make up that shortfall because they are too extreme for a Benny Gantz led government. of course it is possible a dark horse might appear and do that, something like a successful Naftali Bennett return, but I dont think that is something they can count on.