You may have fundamentally missed how the fediverse works.

Lemmy isn't one big site, it's a collection of independent federated servers that share content, with users able to interact across the network regardless of what server hosts their account.

The servers are funded by their owners/users, and can run themselves however they like.

One server going down or going bad would be a loss, but the network as a whole doesn't depend on any one server/server owner.

Unless you host your account on an instance or use an app that advertises, the only ads you'll see on Lemmy are spambots. And if you do see ads because of the first two reasons, you can simply switch your instance/app. (I recommend Thunder for the latter)

Lemmy is open source, it doesn't have an "owner" that could unconditionally inject advertising into any part of how it works.

The hope is that instead of having to ditch the whole thing when it goes bad, going forward, we can ditch only the parts that go bad, and thereby keep the good going instead of having to set up a whole new thing.