Doing it yourself is fine as an educational exercise for newbies, but skilled linux users generally have better things to do than to do the setup by hand for the nth time. On the other hand the “vanilla”/bleeding-edge approach of Arch makes it one of the best bases for derivative distros available, so basing your distro on it is a no-brainer for many.

Twitter probably opened the floodgates when they managed to shaft users and cut API access without outright killing themselves. Now everyone else is emboldened to ask “why can’t we do that too?”.