The main reason being that you have full control of the system, from the kernel, init (OpenRC or SystemD), to the different packages.
I’ve also found Gentoo to be very reliable. (I’ve had some bad experiences with distros like Void with KDE Plasma freezing/crashing).
It’s a rolling release distro, but with more stable package versions, unlike ArchLinux. However it also gives you the option to use the lastest packages (By adding them to accept_keywords)
And if you want you can experiment with different setups, for example using musl instead of GNU’s GLIBC, or using clang as the default compiler instead of GCC.
What is your favorite operating system and what do you like about it?