Why can't the devs just make the transaction fees free unless you want want to prioritize speed and add like a 0.25% yearly inflation as the block reward post 21 million?
It seems it would make the bitcoin more spendable.

I think it is pityful in part of miners if their is no payment in their services. In order for a transaction to be processed and put in a blockchain, miners are the makers of blocks. It is hard for the miners to use current and effort without payment. So I think that is the purpose of fees. To ensure that everyone should be paid.