Forth is a stack-based language, so it does really well on a stack-based CPU. Optimizers for common languages like C perform analysis on which values in a function are more commonly used, and want to control whether those values live in registers or RAM; register based CPU ISAs can give them more fine-grained control.

But if you're working in Forth, everything is stack ops anyway, you wouldn't benefit much from that kind of analysis, and really a stack-based CPU is going to give you the most speed because the most common operations boil down to a single instruction per.

Chuck Moore doesn't mind this because he writes literally everything in Forth. Most of us who work in other languages would mind the performance hit.