Forwarding isn't unlimited, though, as I understand it. The CPU has limited-size queues and buffers through which reordering, forwarding, etc. can happen. So I wouldn't be surprised if using registers well takes pressure off of that machinery and ensures that it works as you expect for the data that isn't in registers.

(Looked around randomly to find example data for this) https://chipsandcheese.com/2022/11/08/amds-zen-4-part-2-memo... claims that Zen 4's store queue only holds 64 entries, for example, and a 512-bit register store eats up two. I can imagine how an algorithm could fill that queue up by juggling enough data.