In football or baseball the league can't handpick your schedule to get you a title.
He got a title shot while avoiding Edgar, Mendes, Lamas, Lentz, Bermudez. Basically anyone with wrestling. Also didn't fight Jeremy Stephens and his frightening knockout power. Nice, safe Dennis Siver, who accidentally took him down twice by stumbling into him.
Then Aldo got injured. Frankie Edgar within seconds was on Twitter campaigning hard for the Interim Title match. And incidentally was the actual listed #1 contender. The only other option anyone was going respect was Chad Mendes, who had recently gotten his second loss to Aldo and would have a tougher cut. Guess who got chosen?
Surprised they didn't just strip Aldo. I mean sure, it would have been less than a year since his last defense, but it would have been the safer play to get McGregor the title, a simple elevation due to stripping.
So anyhow, he took a fight with the only guy you can win the title against (the champion), and won.
Hasn't been seen at 145 since. Probably partly because he is always holding the people who built him hostage for money, and stripping him or having him lose the title would remove their "champions clause" leverage.