It was a failure of leadership. They could have beaten the US and even established an internet first with the OGAS program but funding was cut. https://en.wikipedia.org/wiki/OGAS
At the time the USSR's military R+D was actually decentralised and various different branches were competing with one another. The internet we know was a centralised US military project. Ironically the US won because they had better centralisation.
Another aspect of this was the transition from transistor based architectures to Intergrated Circuit architectures. The US made this transition earlier and faster. The USSR had very little in the way of acceptable Integrated Circuit production, so it was slow to move to the better architecture. They made some really cool stuff like BESM-6, a masterpiece even, but it was transistor based.
To try and catch up they copied IBM and that made them dependent on western technologies so they weren't innovating anymore. The came the microprocessor revolution and they were well and truly behind.
All stems from the root source of failure of leadership to recognise the need to fully commit to it, and also shitty decentralised R+D.
Another factor of this is market. There was no requirement for computers in the USSR outside of Science or Defence. Consider that the entire western computer industry basically evolved from the need for calculators, mostly made by IBM. This was all finance shit. The market for computer innovation was driven by the need for calculation in the market driven economy. This motivation simply did not exist in an economy that was not market driven. There was little need in the Soviet Union to do quarterly projections, calculate capitalisation rates, amortise fixed-costs, etc. All of this drove the production of computers in a way that the USSR simply had no requirement for. In a capitalist economy your entire society has reason to need computers, in a socialist economy only your Science and Defence need it. The capitalists prioritising it faster makes sense when you consider the need would be much more visible for them everywhere in all corners of their system.