Why won’t the merge decrease gas fees?

I have heard that the merge won’t decrease gas fees but it will decrease overall energy use. I’m confused why if moving to proof of stake allows for more transactions to be approved and general throughput, how will this not inherently lead to lower gas fees as more transactions are able to get through?

Also I have heard that layer 2 scaling solutions are what is going to decrease gas fees the most after ethereum 2.0 (or whatever it is called now) is complete. If my understanding is right that layer 2’s are off the main ethereum chain, then why couldn’t these services be implemented now and what changes in the future are planned that makes this impossible to do now but different after the updates?