Is it easy to scale up the fediverse?

The recent ban of X in Brazil caused a huge migration of users to Bluesky.
Around 2 million people joined the "blue butterfly" in a few days without any technical server problems.

The same thing didn't happen with Mastodon a few months ago. In that case, migrations from X caused a lot of problems on the fediverse, with several large and small instances experiencing problems.

Is this a problem with ActivityPub (the protocol behind the fediverse) or a problem with money?

I'm betting on the latter. Most instances are run by tech enthusiasts who ask for donations to pay their server bills.
Bluesky, on the other hand, is a company that can easily expand its infrastructure to accommodate new users.
More users, more value.
That's it!