I think some of the sort-of-obscurity/confusion comes from the fact that, as the OP tweet gets at, you don't really see a very visible "GIS Industry"/products most of the time, you just see tools that happen to have maps embedded in them, and those often require a lot of backend GIS work to power them.
Finding a rideshare and planning your next oil well don't, at first, seem to have a lot in common, but on the backend there may be a surprising amount of overlap.
And I don't know what GIS is. I see it talked about _a lot_ but I don't understand how there can be so much money and interest in geography.
I understand web stuff being huge, because I'm online almost all day. But what _is_ GIS? Is it something businesses do and consumers don't see?