From quick google: "Legacy industries are those that have been around for a long time. These industries dominate a specific market and have not always had a positive approach to innovative ideas."
And I have to strongly agree with OP, I couldn't care less about fate of FAANGs of these days, but I do care about those 'legacy' businesses tremendously.
As for original topic - if it works for 3-4 decades, don't be the stupid guy and change it. Tremendous risk to core business with little to gain.
Relying on the existence of one vendor with highly unportable and unmaintainable code carries its own risk and my post is asking whether it justifies the cost.
I do the same, I have run PosgreSQL for more than 2 decades now and I don't care about portability to any other database, all of which I consider inferior (and yes, I do follow most of their releases).
Google is itself starting to sound a bit like that!