When both RAM (Random Access Memory) and cache memory are transistor-based, why do we need cache memory? Can all applications be run on a single kind of computer memory?

Although random access memory (RAM) is also considered a volatile storage medium, the question arises as to why we would want more cache memory when we already have RAM at our disposal. Is it possible to make all of a computer's storage needs satisfied by a single kind of memory?

Due to the fact that both RAM (Random Access Memory) and volatile memory are transistor-based, it is not clear why cache memory is required. RAM (Random Access Memory) is already available as a volatile memory. Do you think that a computer could operate on a single kind of memory or on several types?

Is associative memory different from regular memory? Which one is more expensive, and why does it cost more?