“They” don’t have that. Most labellers are user made and people can subscribe to them or not.

Feeds are aggregators that show you posts that fulfill certain criteria, such as mentioning keywords (which can include but is not limited to hashtags). They’re a lot more versatile than just hashtags. I can’t tell you why they chose the # symbol to represent feeds ┐⁠(⁠ ⁠∵⁠ ⁠)⁠┌

On your profile you have a following count, that’s where you’ll find a list of people you follow.

The key concept you want to look into is feeds. They’re as, if not more important than hashtags. There’s a feed called Following which is all posts from people you subscribe to.