You're incorrect, this is the normal way that the reddit algorithm functions, it promotes highly-engaging content from niche subreddits.

The top post of all time on r/toledo is about a police officer harassing a woman. It's highly engaging but not overtly political. It has 100x the upvotes of a normal r/toledo post about traffic or what have you.

One of the top posts of all time in r/sanjose is a video of someone trying to jimmy a hotel door open using a hook contraption. Highly engaging, not overtly political.

These were the first two city subreddits I checked. It's literally just how reddit works, highly engaging content bubbles to the top and can reach a much larger audience.