Together with the lack of copyright transfers, it just guarantees the code will always be available under the same license. There can't be any re-licensing of existing code without twisting the arms of every single copyright holder. No more, no less. It gives nobody an exclusive control point. It gives nobody exclusive rights to exploit.

So, yes, Amazon can spin up as many matrix servers as they want. And so can MS. And so can Google. Maybe that wouldn't be such a horrible idea as they have mutually incompatible products that loosely overlap with the matrix feature set; those things interconnecting would be progress. Email is doing pretty OK decades after MS tried to embrace and extend via outlook and exchange. Federated communication networks are nice.

So, that's a feature not a bug.

No. Like BSD and MIT it cannot protect from prorietization, tivoization and SaaS. You need GPLv3 or AGPL for that.

It is a bit more nuanced than that:

The way you wrote it makes it sound like someone can make the project proprietary over night.

They cannot and I wish GPL people would stop pretending.

Whoever has a copy of the repo or even a snapshot of the source can continue using and developing it under the original license.

What one, strong contributor can do is make a proprietary fork and stop contributing towards the original open source one, possibly dumping prices and thereby starving the original project of code and donations.

Gplv3 doesn't protect against saas

That's why I wrote AGPL in the sentence.

Yes, but your sentence suggests either of those would be protective against all of the former.