I don’t think your analogy works, and here’s why.

In that analogy, Reddit provides the beer, but in reality it doesn’t.
It owns the building, but what the customers are consuming are other customer’s beers. It doesn’t have to serve the beer, people being some on their way in.
And in that analogy, yeah, the third-party apps are not on premises, so they can’t watch the ads that pay for the building…
But they brought more clients to the bar. They advertised the heck out of the bar, especially when it was growing, and they pump beer back in the bar. It costs Reddit in ad revenue and in facility maintenance (they built the pipes themselves), but they absolutely get back things through the pipes, it’s just not straight money.

Reddit wasn’t build by Reddit. They own the place, that’s all.

I think it has absolutely nothing to do with Reddit and everything to do with Twitter.
I think they scrambled to get something up and running quickly so they could get the wave of disgruntled Twitter users and jumpstart a new social media for them, and the only feasible option in 5 months was to use Mastodon/Activitypub to get there.
It will be interesting to see how much they give back to the community and if they federate.

They have 30 something mods, they are 4 admins.
It’s not about being selfish, it’s about creating a space that they think can be a safe space. That’s what’s cool about federation, you just use other instances and that’s it.

I’m sure it’s coming soon enough. The federation is such a great concept, interoperability is great!