Because Russians are not Americans.
Normally I wouldn't even waste time defending the US against a statement like that, but give me a break. Throughout its history, Russian leaders have been notorious in terms of their ruthlessness. Do you have anything you want to compare to Stalin's reign? So the American in me says you can find some other gripe to insert in a thread about the Russia/Ukraine conflict.
And OP, I haven't been following the situation too closely as of late but I was kind of wondering the same thing as well. I would have thought that if the Russian resolve to conquer Ukraine was great enough, they would have employed blitzkreig tactics instead of whatever it is they're doing. They've got nuclear capability, FFS, so I don't think I'd be faulted for assuming that any country would rather surrender and not fight than risk something truly terrifying and devastating happening.
I'd be very interested to hear others' opinions on this, too.