I think most MCUs are designed for a specific automotive or other consumer application, against a customer requirement for say 10M chips annually. This is pretty obvious with some chips like Siemens ones that go into ECUs but you rarely see them generally.
That used to be a common practice, but things have changed. Producing a new die is now so expensive vendors want to develop MCUs that can potentially cater to a whole application segment, rather than a particular customer. So they tend to survey customers, and try to figure out a feature set that will have broad enough appeal to capture a number of big players in that application space. Then they make the chip and offer it in their catalogue. This has created some interesting brinkmanship dynamics. Leave out one pin needed by some of the big players, and you can be out of the market. The few cents of extra hardware needed to simulate that missing pin can kill your chances. Throw in a few too many things, and pad out the pin count, and you might be too physically big or too expensive.
But since almost nobody doing that is posting here (not allowed to, for a start) we are talking mostly about lower volume stuff.
You'd be surprised. A number of people here either work or used to work in high volume stuff.