why wasn't support from powerful socialist allies enough to offset it? And why didn't comparable interference cause capitalist states to fail at similar rates?

Support was able to offset it for a while. The USSR was also a fundamental ally to the US and its allies. That period of time legitimized and stabilized their existence so that the Cold War started on a semblance of parity and balance.

The USSR pushed the world towards industrialization, technology development and the Space Race, but it took nearly 50 years of seige to bring the USSR to dissolution.

why didn't comparable interference cause capitalist states to fail at similar rates

The interference simply wasn't comparable. But more importantly the USSR came out of World War 1. The Imperialist capitalist states were already failing and famously there became some fascist states hell bent on destroying all marxism and bolshevism.