Nginx is an absolute beast when it comes to accepting HTTP/1.1 from clients and talking HTTP/1.0 (or HTTP/1.1) to a fixed list of backends or serving files from disk.
Everything else is...hard. Writing plugins - arcane knowledge with next no none documentation. 3rd party plugins, multiple times "acquired" (read: paid the author to work on a new plugin) an open-source plugin and made a much better version available in this plus offering.
gRPC support added only in 2018, http2 support was late, proper web sockets support was late.
Many features that were available "for free" with OpenResty were only on the paid version - good luck writing your own plugin.
They were doomed before F5 probably around round time when they raised series B1 in 2014. All this money and it still had nothing "new" to show. For every Plus plugin, there was most likely a better solution available, and often enough that solution was free or cheaper.
F5 is not to blame, they didn't change anything for the worse. The Plus-license is the problem where essential things like monitoring are behind a paywall. Back then this wasn't so important because you basically only had Apache and nginx.
I think I read two weeks ago what F5 was going to focus more on improving the open source version. Probably because the competition is getting harder and they're noticing it in a market share decline, but whichever the reason is, this was good to hear.
Also it was good to see it no longer being part of a Russian company, even though the devs and owners are good people. You never know how a government can enforce some problematic behavior, specially one which is known for liking to throw people out of high rise windows.
