AIUI, they had to sell. There was no way they could build out the needed infra to maintain the growth rate another year, let alone pay for it.
I thought they had to sell YT because they were starting to get sued into the ground because it was mainly hosting SNL and South Park clips at the time
YT is worth so much because it is a monopoly. To make it monopoly it is today, Google had to have: extremely deep pockets, efficient infrastructure. Very few other companies could have accomplished that.