Why does anyone need to invest at all? Why can't Jack Dorsey just run it instead of needing it be a hockey stick start up?
What's probably true is that if they found a stable source of revenue they wouldn't have to answer these kinds of questions. But this is just back to my original point, of "I don't see how this is going to work", because I don't see how they're going to do that.
I'd be happy if someone jumped in and set me straight with a clear and plausible plan. To me, though, from the information I've seen, it looks like the premise here is that they're going to raise again, and to do that they're going to need to demonstrate accelerating growth, which they starkly do not have right now.
If it helps, nothing I'm saying has anything to do with whether ATProto will succeed. ATProto could succeed (and fulfill one possible overarching goal of the PBC) and Bluesky would still not be a long-term viable forum for scientific communication (because it will stop existing in its current form).