Its basically the difference between buying a consumer car with automatic transmission and self-driving vs putting together a kit car that has manual stick shift.
Ubuntu and fedora and the like, like the modern consumer car, just does everything for you with little hastle. But you might not know anything about how it works and have to call a mechanic to fix it.
Arch and Gentoo and the like, like kit cars, give you granular control over your system, can sometimes be a lot more powerful, is tuned to your specific needs, and most importantly: you learn. You will rarely if ever have to call the mechanic because you know how to just go in and rip and replace or tweak the faulty part.
You can obviously learn to work on your consumer car and start tuning and tweaking it, but you’re not fully in charge.
There are different usecases for different people. For the people who like Arch, installing everything yourself is a value-add, to us it means the system gets out of our way. You set it up one time and it just works.
I put together my install over 6 years ago and have had to do next to no maintenance since then with regular updates.