The feature could be a workaround for a bug. That is, one of their internal services didn't handle being blocked well, and instead of fixing that service they just added that feature as a temporary workaround to make sure the new firewall functionality didn't break any important/core features of MacOS
I'm not saying this is what happened, but without actually knowing what happened we can't assume the intention was to exclude everything in this list forever either.
There's no link because the tweet was deleted soon afterward. The tweet seems to have been very ill-advised.
I don't know how anyone can describe this as a "bug", because as the linked article describes, there's an explicit "ContentFilterExclusionList" in the Info.plist file with a list of the specific Apple services excluded. That's not by accident, it's by design.
I don't think I'd call it a bug. It's a poor decision. I can easily believe that it wasn't a decision made with malicious intent; the culture at Apple seems (at least from the outside, judging by results) to encourage an "it's okay to give our own software special exceptions" mentality.
"The bugs were related to Apple deprecating network kernel extensions (NKEs) in Big Sur and introducing a new system called Network Extension Framework, and Apple engineers not having enough time to iron out all the bugs before the Big Sur launch last fall."
