I hope Bluesky is able to find a model that works for them AND for consumers. (I do know it's an open protocol, so it'll live on without Bluesky itself! However, as this post shows, it's a lot of work to build on the prototype... so if not them, who? And if someone else, how will they become sustainable?)
A) Sustainable revenue is a requirement for any company, yes, but the unlimited (above-inflation) growth demanded by most large corporations is absolutely not. Lots and lots of companies operate for a long time without expecting massive growth, raises n' all. MBAs pejoratively call such companies "lifestyle businesses"--as in "just pays for people to live"--but I'd call them "normal, healthy companies".
B) More fundamentally: the idea that a social media network can only be built by a single corporation owned by investors is an omnipresent, yet extremely toxic, assumption. Mastodon represents another extreme end of the capital<->labor spectrum where anyone can contribute to the network at any time with their own instance, but I think Bluesky is a hint of a less-pure--and therefor more feasible--future.
To use the language of my favorite dream, Chomskian Anarcho-Syndicalism: imagine a social media network organized by a democratic non-profit entity akin to the Python or Linux Foundations, that then contracts out work to a hierarchy of smaller, purpose-built teams ("syndicates"), each of which may in turn contract w/ other teams. Each team would have to attract talent and negotiate enough income to pay them sufficiently still, of course, but there would be no team leader to make a surplus profit from the system -- any "surplus" would stay at the non-profit level, and thus necessarily be reinvested back into the product.
In the current system, the reason Bluesky didn't do this off the bat is obvious: no one would loan them startup funds, as ownership investment is the de facto universal way to start up an unproven venture. But we can dream bigger and better, IMHO; both on a smaller scale by building upon already-proven open protocols like AT Proto, and on a larger scale by structuring the state & economy to support this kind of model equally, if not primarily.
I always look at how WhatsApp played out as the company. They were the good guys, and didn't want to get acquired. Zuckerberg, almost bankrupt FB at the time giving into all of the ridiculous demands WhatsApp made. No one at WhatsApp thought it was going to happen, until it did and did result in a once-in-a-lifetime transfer of wealth to several hundred employees.