There are lots of users’ made algorithms and the main feed is one of them by the Bluesky, you can unsubscribe to it (AFAIK), I have one for myself and anyone else interested in the said topic of it.

The main feed also can mix every other feed you signed up for.

You answered yourself, if you don’t see the brand, that brand didn’t paid for the exposition.

This thumb gave me Cesar3 vibes, I liked it