That’s probably the reason. It was the 70s and 80s for me, I was technically an adult by the mid-80s. And my recollection is that they were definitely on a downslide back then, becoming rarer and produced more erratically than when I was a kid/teenager. That was one of the reasons I switched to US editions, after all, so it wasn’t all just me losing interest.
And in the 90s I still met a lot of comics who read American superhero comics (and that new guy, Gaiman).
It was never something that “everybody” did, like watching Lassie or Ein Cold für alle Fälle, more on the line of reading pulp SF like Perry Rhodan or SF in general.