Can someone more experienced in self hosting explain why I would wanted a dedicated prosumer NAS over just a regular tower with a bunch of drives? I understand why someone working at a data center might want a rack mount NAS full of drives. But the desktop NAS models you see on like Newegg don’t immediately strike me as special.

It's an appliance. You stick it in the back of a closet and you forget about it. There's a company dedicated to providing updates, and reducing interference during upgrades.

So if you just want something to work, having a company that guarantees it just works is very valuable