Soviets ruled only until 91. So those 50 years speak more about the collapse thereafter. And the cream of their mathematicians emigrating to Israel.

The poster above that mentioned commercialization has it right - while the soviet science was often top-notch, the skills in commercialization and getting the finances to get things done were simply not there, severely eroded by the decades of Soviet time.

The Soviet Union existed for less than half of that time period, and a lot of talented researchers moved to the West after it collapsed. (I know because I've worked with a lot of them). So that's kind of a weird time period to sample. It's like saying if Einstein was so smart, how come he hasn't published anything recently?

Considering 35 of these 50 years is quite literally not the Soviet Union, that list is still long: https://en.wikipedia.org/wiki/Timeline_of_Russian_innovation