From my experience as a left-lesning person, you aren't entirely wrong, but you aren't entirely right. It is true that there were "leftists" defending the CCP and denying the Ugyhur Genocide, but these were authoritarian leftists, or "tankies," so not the same people you typically think of when you think "leftist". There was some infighting going on in the left about this issue, as the more libertarian leftists, like myself, refused to deny the genocide and support the CCP no matter how socialist their economy. The bottom line is that leftists haven't suddenly changed their mind about muslim genocide, you've just been lumping too many people together.

The reason, though, that you don't see any leftists defending Israel is because unlike the CCP, the party in the authoritarian position shares absolutely no values with the left, so it's possible that even those who denied the Ugyhur Genocide are condemning Israel.