I think they took it directly from here: https://webkeks.org/objfw/ which does say 2012 as the last release. I see on GH they have commits from as recent as last month.
The problem is not the syntax support. The ObjC runtime had many changes to it done internally over obscure flags to support Swift and other compiler features. These are not readily documented on Apple open sources. (Perhaps more documentation exists in LLVM.) Once the runtime contains ABI changes, it makes it difficult to port apps that (ab)use the runtime. Not a problem for some apps, but a big problem for others.
The problem is not the syntax support. The ObjC runtime had many changes to it done internally over obscure flags to support Swift and other compiler features. These are not readily documented on Apple open sources. (Perhaps more documentation exists in LLVM.) Once the runtime contains ABI changes, it makes it difficult to port apps that (ab)use the runtime. Not a problem for some apps, but a big problem for others.