Same story as Vice City, same rights holder, same takedowns.
San Andreas benefited from the same reverse-engineering effort that produced the browser ports of GTA 3 and Vice City. It ran in a browser. It was also the largest target of the three.
Take-Two's enforcement against the reverse-engineered GTA source was aimed at the underlying code, not just a single hosting site, which means any mirror tends to disappear and reappear.
If you want to play San Andreas, the version Rockstar sells is the one that stays working.