South Africa pledged only 176,000 to UNRWA in the year 2022, the last year a full list of donors was provided by the UN.
Like the Arab states they understand that to give money to UNRWA is to give it to the corrupt leadership of both Hamas and the PA.
Plus the Arab states know that Hamas is a radical branch of the fundamentalist Muslim Brotherhood which seeks the overthrow of their own regimes.
So it’s fairly clear why they pledge little and give even less. It’s the same reason they refuse to accept Palestinians into their own societies, either as refugees or citizens.