Because the left has decided giving money to Ukraine is Good™ therefore anyone who has any other ideas about the situation is Bad™. Not to mention it’s members of the party of Evil™ who believe something Bad™.

Personally I’m for donating to Ukraine.

You don’t have to agree with them, but there are valid reasons:

• Representation: My constitutes don’t want X and I’m here to represent them.
• Problems at home: We have a shitload of problems at home that could use that money.
• Budgetary: If you think the debt / deficit is a pressing concern, see “Problems at home”.
• The Russians are the Good Guys™ (Takes some mental gymnastics to get there)
• Escalation: Funding one side could lead to a bigger conflict
• Isolationism: Not our problem. We’re not the world’s police
• Pacifism: No violence, ever.

And some not quite so valid “reasons”:

• The “other side” wants it, so I’ll vote against it
• My campaign contributor needs something.
• This will help me get into the news/votes!
• I can use this vote later to prove i’m not a “war hawk”.
• I got paid a lot!

It can sometimes be hard to tell if a person’s given reason matches their true reason, sometimes it’s not. Your existing biases will influence what you think about that.