When you build websites on a regular basis, it is nice to have a certain Top Level Domain (TLD) to point at your development machine. For example, every domain ending in ".dev" or ".loc" should automatically point to your machine.
So as a Gentoo sysadmin you would like to keep your system clean. But sometimes you also like to do some experiments. For example, you want the stable version of PHP on your system, but you want to check out the latest version. Gentoo allows you to pull in both 7.4 and 8.0 and use them along with each other.
There are literally thousands of distro's available of which some of the most popular are very user friendly, have a great community, are stable and secure and have tons of software available in their repositories. So why would you choose a distro that is way harder to install and maintain?
Finaly I have my own Gentoo production server up and running (by the way, I'm not using Arch ;).