How do I add a Files section on an Accounts main page like there is on an opportunity?

That’s a good question! The Files related list usually has to be added manually through the page layout or Lightning App Builder. You can go to the Account Page Layout, select Related Lists, and then drag the Files option onto the layout—similar to how it appears on opportunities. If you’re working in Lightning, open the Lightning Record Page for Accounts, add the Related List – Single or Related List – Files

component, and save it. That should give you the same section. 

By the way, I recently came across a discussion about organizing digital assets for a