Under an Islamic rule, the Muslim is forced to do this donation. And Muslim billionaires are not all of a sudden all pious because they have this label. Islamic law doesn't eliminate the need to study politics and sociology you know. Many Muslim scholars, claimed that it could in fact end the poverty in the Islamic world if really all obliged muslims paid their zakat (which is a requirement for Islam, not like a side quest, and should be enforced legally), among them Dr. Abd Al-Rahman bin Hamood Al-Sumait a humanitarian. This might appeal to you?: https://www.theguardian.com/global-development-professionals-network/2017/jun/22/zakat-requires-muslims-to-donate-25-of-their-wealth-could-this-end-poverty