To put a bit more context to his work, at the time, "genetics" wasn't really a science, still in its infancy, and "darwinism" was irrevocably linked with "social darwinism" which was favoured quite heavily by the USSR's western neighbours. The two were interlinked heavily at the time, so to accept the idea of "darwinism" would also mean accepting that some races of people were more "evolved" than others. This is of course wrong, but at the time it was the commonly held belief.
So you had a country that pushed the idea of true equality, but the bourgeoise science of the day insisted that some groups were inherently inferior to others. It makes sense the USSR would give a lot of pushback to this idea, and heavily promote the ideas of a man who believed it was incorrect.
This was before the discovery of genes and any understanding of DNA, and interestingly enough, Lysenko's work, while ultimately flawed in its conclusions, may have accidentally discovered the science of "epigenetics" decades before anyone else had. They lacked the framework to understand it at the time, which is why his work is often claimed to be based on "Lamarkian evolution" when in reality, it was original, albeit incorrect, theories.
Scientific thought doesn't mean "being right 100% of the time all the time" it means "challenging if what we know is actually right or not." So while it is easy to dismiss Lysenko with hindsight, at the time he wasn't doing "bad" science at all. Hell, a good part of the proofs for darwinian evolution came from people like Lysenko attempt to disprove the theory.