That's because UNWRA isn't the UN. Really the UN should have sent proper members there instead of making a special case and creating the UNWRA in the first place.
UNRWA is part of the UN, same as UNHCR. It's development and continuation separate to UNHCR has to do with denying Palestinians Right of Return. The most recent false accusations are used by Israel to futher destroy and cripple any aid infrastructure for Gaza. To intentionally force millions to suffer from famine, disease, and dehydration.
"UNRWA was established in 1949 by the UN General Assembly (UNGA) to provide relief to all refugees resulting from the 1948 conflict. It also provided relief to Jewish and Arab Palestine refugees inside the State of Israel following the 1948 conflict until the Israeli government took over responsibility for them in 1952.[7][8][9] As a subsidiary body of the UNGA, UNRWA's mandate is subject to periodic renewal every three years; it has consistently been extended since its founding, most recently until 30 June 2026.[10]"