The causal chain is fairly simple. The RSF are proxies of the UAE (and therefore of Israel). With the latter now busy with Iranian attacks they cannot afford the attention or resources to support their pet project in Sudan anymore.

The RSF never had organic support in Sudan. They are genocidal, murderous maniacs despised by most of the Sudanese people. They have been armed, funded and propped up by imperialist interests just like ISIS was.