“No loops” was done for safety reasons. https://www.cs.princeton.edu/courses/archive/fall05/cos518/p..., section 3.5:

“To prevent DIF from inducing an infinite loop in probe context, only forward branches are permitted. This safety provision may seem draconian — it eliminates loops altogether — but in practice we have not discovered it to present a serious limitation”

And we disagree about what can be called “a dtrace reimplementation”. Because there’s decades of prior art on tracing, I wouldn’t call anything that allows looping that.