Why is that so mind blowing? Microsoft has a gigantic market share in basically every vertical. There are tons of software companies who make Windows-only products. The world is bigger than (and in fact is largely not) FAANG and startups.
What's a "vertical" in this context? The article uses it as well, but also doesn't explain. This is the first time I've heard the word used this way, and it's a tough one to search for.
But here it's actually overspecified. Parent probably wanted to simply say that Microsoft has a gigantic market share in basically every industry sector.
The word you're looking for is probably "prosaic".
A large chunk of people making iPhone apps is basically tied into the feature set given to you by Apple that you leverage to make a product on top of. Same with Android.