It isn’t just that. The design philosophy of the Russian equipment is very different than ours. We design ours to be serviceable, maintainable, and repairable for rather long lifetime in times of war AND peace,often at the cost of initial cost and performance. Russian equipment is designed to be running much closer to the edge, and generally needs more upkeep and parts. Running lightly-built, highly stressed planes and engines near the edge was one of the reasons that the Russian planes looked pretty darned good on paper vs ours for years (and still do).
Oddly enough, there is a perverse unintended consequence of this. If you buy aircraft from the Russians, you had better have a price-controlled contract and be on good political terms with them as long as you plan on using then, because otherwise your fancy plane will be doing gate duty at the local public park in no time. On the other hand, US equipment is much easier to get (or even make)parts for, and has great training and documentation. Ask the Iraqi’s about their MIG’s at the dawn of the gulf wars. Then, ask the Iranians how their Shah-era planes are holding up these days. Amazingly well, I have read.