OCHA-OPT (the committee gathering this data) is strict about verifying validity of Palestinian casualties, requiring two independent, verified and non-affiliated sources. Casualties in Israel, however, they trust the media at face value. They also exclude a lot of Palestinian casualties even when verified in certain situations. Example, and I quote them:

People who were killed or injured in conflict-related incidents that took place in Israel and did not involve residents of the oPt are also excluded.

oPt (occupied Palestinian territories) are the areas that Israel does not directly oversee. So most of Israel is not oPt by their criteria.

Israel is notorious for restricting journalists reporting on Israeli crimes, and has murdered journalists countless of times, like last year the Christian Palestinian Shireen Abu Akleh reporting on the forced expulsion of Palestinians from Sheikh Jarrah (so not even in a war zone area). This causes many casualties to go unverified and thus undocumented.

And Israel has been caught lying before about its own casualties, like the 40 beheaded babies.

Take that as you will.