Not giving updates and not allowing customers to create new instances is one thing, and is normally how these big deprecations are done. Outright destroying your customers' data just because they didn't migrate in time is wild (and its very easy for something like a database migration to take much longer than 2 years).
That old IBM one?
[0] https://en.wikipedia.org/wiki/IBM_Information_Management_Sys...
I don't know anything about this, but I'm near this on the postgres side of azure. On that end I've seen a couple transparent migrations & have been working on less transparent ones too (such as pg11 eol). This handling of mariadb casts a bad light on the db services as a whole that doesn't match what I've seen previously