My understanding is:

1. Ukraine forces know how to pilot MIG29s

2. Poland has MIG-29s, USA does not

3. Poland has time to retrain on newer equipment, Ukraine does not

4. Poland doesn't want to be defenseless, if it gives aircraft to Ukraine.

So Poland gives Ukraine exactly what they need right now... USA agrees to aid Poland in replacement aircraft.

This isn't about "USA didn't give Ukraine aircraft", Poland did! It's about getting Ukraine the aircraft they know how to use right now