I’m not aware of any studies on this, so anecdote is all I have. But for me, it’s “obvious” that politics is a factor rather than “obvious” that tourists only think of trends and exchange rates.
In fact, it’s now common (at least in my circle) for people to plan vacations to avoid changing planes in the USA, because of the delays in customs and the risks of missing connections or being denied entry to the US (required in the USA even if you never leave the transfer area).
Is it true that they must clear customs _in addition to_ passport/immigration control? If so that is indeed unusual.
If you had flown into Amsterdam and transited to Moscow you would have gone thru metal detectors to the departure lounge, but not thru immigration