Clash Royale is popular? Sampling my entire social sphere: around where I live, everyone and their dog plays or at least briefly played Pokemon Go. Clash Royale is a title I know only from the constant advertising spam on Facebook; I haven't seen a single person playing it ever.
I know it's just a local sample, but for something supposedly more popular than Pokemon Go, I'd expect to encounter at least one player.
pokemon go is a much more "visible" game. if you have any idea how the game works, it's really obvious when you see people playing it irl. it's hard to notice people playing clash royale unless you look at their screen or hear them talking about specific cards from the game. when I was waiting for a flight at the airport recently, almost all the kids seemed to be playing clash royale.
anecdotally, I don't notice clash royale being as popular with adults as pokemon go. it may be true that it's not very popular in your world, if you don't spend a lot of time around children/teenagers. in my bubble, I hardly ever see people playing pokemon go anymore.
The game was insanely popular for the few weeks immediately following launch in 2016. It is entirely possible that Clash had more players, but they weren't all outside walking around while looking at their phones in places they'd never visited before.