Because they are in an endless war that they can't get out of and which is draining their economy?
I really don't think that Russia anticipated this being the situation three years ago. I suspect that there are many on their side that are hoping for an end to the war that saves face for Russia.
Because they are in an endless war that they can't get out of and which is draining their economy?
If Trump stops funding then the war won't be "endless".
Trump and his voters want the war defunded. Putin knows that. Trump would have to bluff and threaten further funding, else Putin will take from Ukraine what he wants.
The US wants out.
That leaves Ukraine as dead meat hanging.
Russia hold all the cards.