Core devs are how we typically refer to devs working on Bitcoin Core. Bitcoin Core is one implementation of a Bitcoin node, although it’s by far the most popular. The code for Bitcoin Core is hosted on GitHub, a platform owned by Microsoft.

The people who give the final say on changes to Bitcoin Core are the maintainers. A controversial change was proposed and someone got banned after egging on something a maintainer said was off-topic.

Now people are angry because they are just now realizing the development of Bitcoin Core is not democratic. This isn’t a problem imo since Bitcoin Core doesn’t define the protocol, but I believe the anger stems from people who do implicitly see them as the only de facto implementation of the protocol.