Why is US train travel so much slower than that in Russia of all places.

In short, the car industry and car culture won out here. A lot of public transit is seen as for the poor and other disfavored groups. The US right complains endlessly about Amtrak subsidies, while somehow ignoring the half-trillion dollars (per Wikipedia) spent on the interstate system (plus lots more spending at the state for highways, etc).

US train companies are allergic to capital investment. Essentially no electrification, limited double tracking, passing sidings too short for the 2 mile+ freight trains, and essentially no alignment upgrades to increase running speed. Then we put a precision scheduled railway (PSR) operational model on top of it which incorporates none of these words => basically freight trains move ad-hoc when they are ready. This is why Amtrak service in the west can be 18 hours+ behind schedule.

In Russia, the entire Trans-Siberian Railroad is electrified and almost entirely double tracked.

The US makes very good use of its extensive rail system but they use it for astonishing amounts of cargo, not for moving around small numbers of people very quickly. Outside of perhaps the Boston/DC corridor, passenger rail service is about enjoying the scenery. For any other use, cars, buses, and airplanes are better in most ways.

No high speed rail.

CAHSR will cover more ground than Moscow-St. Petersburg in less time... if it can be completed, which given the political headwinds is a big "if."