Why parameters stored in registers and not on the stack in x86-64 Assembly?

Question

In x86-32 assembly, parameters are stored on the stack but in x86-64, parameters stored in registers. What is the reason for this?

Answer 1

It is (a lot) faster to access CPU registers than to access RAM.

Since 64bit CPU have a lot more general purpose registers (has nothing to do with being 64bit, it's just because they are newer/bigger), it makes sense to make use of them.