why not netrw?

I don't know it. I tend to prefer vanilla setups with minimal customization, so it's very rare that I look at what plugins or add-ons or mods are available. NERDTree came to me by way of coworker, and I've grown to like it enough to put it in when I go to a new setup.

From the name... I'm guessing it lets you vim into a remote? (Looked it up; basically, yup.) That doesn't sound useful for my purposes. I prefer to SSH in and boot up an instance of vim on the server. Preferring vanilla makes that not such a bad thing. :P

netrw is actually a built in, not a plugin and acts as a file browser like NERDtree.

That said, I've never found netrw's behavior to be as friendly as NERDtree's at least out of the box.