Just because the egg/wheel format existed, didn't mean that they where actually used and actually worked. Being able to reliable pip install packages like numpy and gdal only started 3-4 years ago. There is a reason that Christoph Gohlke's python package site exists and was popular.

I started using numpy around 2007 and didn’t see reliable binary installs with good numerical performance until I discovered anaconda, much later (2016?). Maybe I hung out with the wrong people, or libraries. Some libraries did not have compiled wheels a few years ago, and M1 macs still run into the very occasional issue.

9 out of the top 360 packages still do not offer wheels! https://pythonwheels.com/

Not having a wheel is not really an issue for Python-only packages.

You’re running install-time code if you don’t, so I disagree. The wheel format is better suited even for pure python distribution. You can read more details on that site.