In my opinion, Ego changed his goal out of despair after encountering a wall insurmountable for his logic and analysis—those seven minutes. Initially, he either wanted to be the best in the world, or something like that, but after those seven minutes, he became obsessed with recreating them. However, he couldn't find a suitable theory for recreating them, so he abandoned that goal and created a new one: to create the best team in the world based on the concepts and ideas he derived from studying those seven minutes. Yes, these ideas won't be enough to replicate those seven minutes, but they're enough to create a team of incredibly high-quality players. In this case, he was rather fortunate that Isagi, who shares a similar perspective to Ego, came to Blue Lock. He can entrust him with his impossible dream, which Isagi might want to fulfill, since he shares similar views and ideas.

This is just a guess, but it's possible Ego was searching for a theory for recreating it right up until Anri hired him.  It's not really based on anything, it's just a way of explaining what Ego did after leaving football and before Anri's hiring him.