Assembly uses more than registers.

And unlike registers and memory addresses, you don't really have to juggle regular variables in your head unless the program has a lot of unnecessary mutability, or really bad variable names.

> number of variables any half complicated code has.

It is not about sheer number of variables some code has.

It's about how many variables we have to fit in our head in order to understand some flow or calculation.

x64 has 16 general-purpose registers. "Much lower" starts somewhere around a half. I say, touching 32 variables in a given scope is not "half complicated", it's sabotage.