This, it's really interesting how unenthusiastic Obama is. There are a few different possibilities as to the cause:
1. He has very low confidence in a Biden win. All he really cares about is his image and legacy, hence not wanting to hitch his wagon to losers. Other Democrats act in a similar way. If they were confident that Biden would crush Trump and triumph gloriously, they should all be parading behind him so they can share in the glory of Orange Man Out.
2. He's pissed at the Democrats and is only willing to do the bare minimum of endorsing necessary so that people don't start asking questions about "where's Obama?" It's known there's bad blood between him and the party, he was one of the worst party leaders ever with the Dems losing hundreds of seats in Congress and literally over a thousand state-level seats under him and he almost bankrupted the party running vanity campaigns trying to turn red states b;ie.
I'm surprised they haven't found some way to persuade him to help more. A big round of Obama-led Biden rallies might actually attract crowds they wouldn't have to use trick camera angles to exaggerate the size of.