Hersh is well connected to the Russian intelligence agencies and has been for his entire career, including before the recently very viable "Debunking" of his Syria story-line (another story that benefited Russia). He's publicly stated he is close friends with Scott Ritter, who recently called for Ukraine's "annihilation", and both are regular guests on propaganda organ RT.

Hersh's previous activity played a key role in eliminating support for anti-Russian forces in Syria. Hundreds of thousands are dying in Ukraine right now. I think it's pretty obvious exactly why Russia would want want to pin these explosions on the USA, and why the USA would take steps to ensure the truth came out,