He didn't care about Leon until there was some benefit in fighting him?
I don't even think Nate Diaz was ranked, so Leon's only top 10 win was 3 years before he fought for the title.
Colby beat #7, #3, #1, #5 and #6 and had 2 FOTY candidates with the champ, and wasn't given any immediate rematches, he fought to keep his spot after each.
Khamzat would have been next, but couldn't make weight and seems to be going to 185 now, so it's Colby, who’s been the consensus best guy after the champ for 4 years.
If he wasn't, Leon wouldn't be trying to duck him, and you'd be betting all your money on Leon when they fight, but you're not, and Leon is trying to "defend" against a guy Colby dominated, and already got 2 title shots himself and lost bady in both.