Why people say "I was wondering if...

why people say “I was wondering if …” not "I am wodering if … "?
Thanks.

They say both. I think that putting a request or question in the past makes it sound more polite, much as putting it in the conditional would.

“I’m wondering if you’ll help me,” sounds a little abrupt. It sounds more diplomatic if it is changed to “I was wondering if you would help me.”