Ok, here's the thing.
I'm going to put aside my views on both Israel and Palestine, along with whether or not I agree with Biden's handling of the situation.
But let's be realistic. The jewish population in the US is a bit over 7.5 million people. There's roughly 250,000 Palestinians in the US. Biden withdrawing support from Israel may very well be the right thing to do. But instead of the Palestinians and their supporters protesting, it would be the Jewish population and their supporters, which is far, far larger. Biden's numbers would be even lower than they are now, the protests would be far larger than they are now, and antisemitism would spiral out of control. If the Jewish population were to withdraw support for Biden as much as the Palestinians did, Biden might as well drop out of the race and hand Trump the presidency on a silver platter.
From a political point of view, Biden is in a no-win situation. This is what happened because he chose to side with Israel. It would be worse for him if he supported Palestine from day one and got flack from the Jewish population. And if he keeps flip-flopping, he'll end up just pissing both groups off.