I've never been into Doom clones (to use the term from back in the day) and yet I have enjoyed playing countless video games from about 1984 through to the present. Very few of them are first-person games, whether they're head-clickers or other forms of first-person gaming.
AAA companies might pump out a lot of FPS- though it's arguable that they also grind out all sorts of other reliable and less-than-groundbreaking genres, from flavor of the decade trends (MMORPGs/MOBAs/live service battle royales/extraction shooters) to annual sports titles to Assassin's Creed sequels. The Call of Duty machine aside, I'm not sure if FPS is as much of a cash cow as it used to be.
And if you look at this best-selling video games list, there's only a single FPS in the top ten (PUBG, which is technically also third-person):
It might be that they're targeting the 8 - 18 year old boy demographic, and that's always a huge cash cow, whereas older gamers have refined taste but don't spend that much money on games because they don't spend that many hours on gaming
