The Fediverse’s biggest onboarding problem is having too many choices that seem important but don’t really matter. Namely, which instance to sign up on. Listing two different platforms that do the same thing and even federate with each other would only make it worse. I’m guessing that’s why they only listed one.
As for why choose one over the other, I don’t have a horse in this race, I’m sure they had their reasons.
Yeah, you’re right, and that sucks. Mastodon is much better at this.