The fediverse already has a mechanism to guard against some corporation coming in and taking the code from a platform and building a commercial product on top of it - defederation. We don’t need GPL to “protect” us from anyone here

I disagree. The reason GPL works is that legal action (Such as from GNU foundation or EFF) deters bad actors.

The fediverse already has a mechanism to guard against some corporation coming in and taking the code from a platform and building a commercial product on top of it - defederation.

Defederation only helps the corporations: When the corporation comes in, overwhelms the fediverse with their huge network of active instances and then defederate, the only ones holding the bag are the open intances. . It’s much easier for a private corporation to get numbers to defederate and come out on top than for open source enthusiasts.

However, there are also many that want to be recognized (financially) for their work. GPL ignores the latter.

If you want to be financially recognized for building on top of other people’s open source projects then you should write proprietary code. You shouldn’t be allowed to take open source works freely and call the entirety your own. MIT doesn’t prevent that from happening. GPL prevents that from happening.

I don’t believe that is the case any more

It’s actually really important in the long run. There can never be true open source without GPL or similar legal licenses.