> It was an overall improvement than those and therefore there is a legit reason for it to take off.

Of course. The rate of adoption is related to the increase in value compared to the status quo, much like how genes spread. But Rust's adoption is slow precisely because its "fitness benefit" is low.

> That would almost always cause problems but for greenfield projects it's a no brainer IMO.

It would have been a no brainer if, when writing a new codebase expected to last 20 years or more (which is often the case with software written in low-level languages), you'd believe the chosen language to be very popular over the next few deacdes. But given its slow adoption compared to languages that ended up achieving that status, despite it's rather old age, it's not looking like a safe bet, which is why Rust's adoption for important greenfield projects is also low (again, relative to other languages).