What use does cache memory serve if random access memory (RAM) also uses transistors? Is there a single memory type that benefits everyone equally?

The rationale behind the inclusion of cache memory in computer systems is not clear to me, given that transistors are utilised in the construction of both random access memory (RAM) and read-only memory (ROM).Temporary storage can be conceptualised as a transiently available form of RAM (random access memory). Can one envision a computing device that solely relies on a single type of memory?

The topic of why we need cache memory when we already have RAM (Random Access Memory) as a volatile memory naturally arises given that both cache memory and RAM employ transistors as its fundamental structural component. This is because the main structural element of both RAM and cache memory are transistors. Is it feasible to use a single form of memory to serve all of the computer's varied needs, or are many types of memory necessary?

If random access memory (RAM) also uses transistors, then what is the point of caching memory? Is it possible for a single form of memory to accommodate all uses?