How does Reddit have the biggest communities online, while having way fewer overall users compared to other social media?

Just a few random examples: Taylor Swift, accounting, building decks for your house.

Why are the main communities for such topics located on Reddit rather than any of the way more popular social media? Tiktok has a little over double Reddit's active userbase. Instagram and Facebook both have triple.

Despite this it is almost always Reddit I hear mentioned as the main place researchers, youtubers, podcasters, journalists, etc are using for their info gathering.