#3 Because Brock Lesnar is otherwise occupied for now
Deep down in our hearts, we all wanted to see The Fiend take on Brock Lesnar in an actual dream match. Because both men are powerhouses, there would have been no way to tell who would have come out on top during the contest.
But, instead, we have Brock Lesnar taking on Rey Mysterio with the WWE Championship on the line. So because there isn't a real Number 1 Contender per se, for The Fiend, Daniel Bryan seems like the ideal candidate for now.
Roman Reigns is currently otherwise occupied with King Corbin and I guess that's a feud that will last for a pretty long time. Kofi Kingston is in the tag team division and it looks like that is where he will be for the foreseeable future.
I don't think it seems like The Miz is Universal Championship level ready yet, if you round-up all the babyfaces.