Why don't combos work?

I think the main problem with combos not working is that one skill doesn't imply additional damage from another skill. It's worth citing a simple mechanic, such as Clair Obscur. If, for example, some shots were generators and others were triggers (which, of course, could be modified and changed), everyone would want to maximize their damage by creating such a combo. Furthermore, such a change would weaken many attacks when used alone, making the game more difficult. Then there wouldn't be a need to add so many mobs, which, in my opinion, ruin meaningful combat. And I know that "by name," such solutions are being implemented, but it doesn't quite work because, by definition, every skill can be maximized. In addition resistances - this type of solution was in Diablo 2 - some mobs were simply completely or almost completely resistant to a certain type of damage, which forced the player to rotate skills.