Looks like people extending rust never really focused on compile speed when designing features (from [1]):

> If you could reinvent/change any aspect of Rust, what would you do alternatively?

> A lot happened because we wanted to ship a useful thing with only so much time in the day, so some things were less deliberate than others. There’s an alternate version of Rust with significantly faster compiler times, because while we cared about compile times when designing we always prioritized other values more. We never asked ourselves how this feature or implementation impacted compiler analysis time and there are several spots where something slightly different would have much faster compiler times, which people do care about. But had we spent time on that, we would have neglected other things and not been any more successful.

[1]: https://alexalejandre.com/interviews/interview-with-steve-kl...