The context you’re missing is the existence of the holodomor.
They had been dominated and literally genocideded by Russia leading up to WWII.
ANYBODY who shows up to kick out the people who genocided you is going to look pretty attractive in that moment.
Asking a Ukrainian to side with Russian occupation in 1941 is like asking a Jewish person to agree be occupied by Germans in 1949. It’s a tough sell when the pain is that fresh.
Anyhow, I’m not saying anything about right or wrong, just the historical context. It’s hard to understand Ukraine without understanding the Holodomor.