It's in the career trajectory of every comic actor working. Sooner or later, the actor actually has to, well, act.
Audiences are fickle.
When Michael J. Fox, Chevy Chase and Mike Myers tried to dig a little deeper, the paying masses turned the other way. A subliminal message was sent to his comic brethren. It's okay, guys. You don't have to make 'em laugh all the time. But make 'em cry.