> I ask people to design a system but the system itself is very write heavy. Like 50 writes per read imbalanced. People will often suggest a cache because it's in the standard interview prep but not actually think about why they need it.

I mean, it's a cool thought process to go "Ooh, maybe I can store up repeated things so I don't need to repeat an expensive access process often!" It's a byproduct of modern computing hardware that we frequently have the luxury of not thinking about caching very often.

I don't think you should punish people for considering a cache. Write caching is a thing, it might just not be applicable for the system you're considering.