Kitchen Sinks Stainless Steel
When you state "cooking other kinds of food" I think what you truly suggest is other kinds of cooking. So when searing a steak in your cast iron you're asking "why is this not steel"
Well many of your quality pans you utilize in the kitchen area will be stainless-steel (or stainless sandwiched in between other metals or other metals sandwiched in between stainless). Inexpensive ones might be aluminum.
Stainless Steel Kitchen Cupboard
Aluminum is the worst because it moves heat TOO quickly developing hot areas in your pan and unequal cooking. Thats why cast iron is favored for things like searing stakes, the cast iron is thicc, holds heat, is a poor conductor compared to aluminum which enables the pan to heat more equally.
So the short response is you're probably currently using stainless steel pans, pots, and so on. We use cast iron frying pans because they are inexpensive, heavy and heat really evenly.