Not all CPUs do register renaming, and almost all architectures will have started out being defined for a CPU which didn't do renaming. Even today, lower end CPUs (think the embedded market) don't do register renaming. If you want your architecture to be able to cover down to the low end then anything that drops the idea of a register file is a non-starter. Also, a register-based architecture is well understood, in terms of how to implement it effectively, how to exploit it in compiler design, and how to hand-code assembly for it when necessary. You need a really strong argument to justify taking the weird and innovative route, usually.
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Not all CPUs do register renaming, and almost all architectures will have started out being defined for a CPU which didn't do renaming. Even today, lower end CPUs (think the embedded market) don't do register renaming. If you want your architecture to be able to cover down to the low end then anything that drops the idea of a register file is a non-starter. Also, a register-based architecture is well understood, in terms of how to implement it effectively, how to exploit it in compiler design, and how to hand-code assembly for it when necessary. You need a really strong argument to justify taking the weird and innovative route, usually.