That’s exactly how a backlog of transactions incentivizes more hashing (more precise term than calculation). Block production slows down, meaning more transactions bid for the next block, meaning the fees they bid go up.

In our current epoch, the block reward is bigger than the fees, but this will change much sooner than people realize (10-20 years from now if demand for blockspace simply remains constant)

There is a supply and demand relationship for blockspace, with a hard limitation imposed by the difficulty adjustment.

The difficulty adjustment also causes the blockchain to be a reliable notarization service - 10 years of blocks can only be made over 10 years. And that’s really what this whole system is - an (effectively) immutable notary