"Why are you on mastodon.social?"
I get this question a lot. The simple answer: I've had this account for 4.5 years. Back then, mastodon.social was not so big.
I use this instance because it's maintained by @Gargron and we talk often enough.
Sometimes we disagree, but I like have access to "vanilla" Mastodon.
But I'm also elsewhere. I'm on *many* instances. Some are hosted by others, some are hosted by myself.
I don't even consider this my "primary" account -- just the most visible.