You never saw the original ghostbusters movies? Or little shop of horrors? Or plenty of other things.
The thing about Rick Moranis is that while many people will instantly recognize his face, they won't necessarily be able to connect it with a name.
He's a bit like Al Leong or Thomas F. Wilson in that regard - those names might not mean much to you, but if I had written "Biff Tannen" or "that Asian-looking henchman with the goatee (Uli from "Die Hard")", they're the people whose faces would have popped up in your head.
Moranis is the kind of actor who got cast to play the stereotypical target of a bully, somewhat timid, insecure and mousey. If his name is in the credits, you can almost be sure that there will at least (!) one bully in the movie who is going to pick on the character Mornis is playing - that is, until he gets pushed too hard and confronts his tormentor. "Spaceballs" is the rare exception to this rule, because Mel Brooks is a genius.
Moranis taught an entire generation of kids to stand up to bullies and it's really sad he disappeared from public life in the 1990s, even more so because of the reason behind this decision. I wish he had been able to continue his work, maybe it could have counter-acted the normalization of cruelty and oppressive behaviour that happened after Bush II became president and shows like "The Apprentice" became popular.
Which coincidentally brings us back to Trump.