He became convinced that boxing could work in MMA when most doubted it. Had some success on the feet. He also had a little success there. You basically just said "I don't agree" with no support for your stance.
If you think it's because he couldn't take people down that he abandoned grappling, I guarantee that if he put his mind to it, he could've improved enough to remain/once again become a serious threat to take guys down.
If you argue the BJ fight, same shit. BJ easily was one of the best at TDD in those days.
He was standing and banging for many years. He came to the UFC during the time when that became encouraged.
I'm pretty confident "sure that's how it happened" for the majority of grapplers who decided they'd become boxers/kickboxers instead of honing their takedowns and adding setups.
Or are we going with the staph infection as the cause of Diego falling in love with brawling?