I'm about to go on a rant. I'd like to apologize before I even start.
If Daniel Bryan had not returned before the 2015 Royal Rumble, then Roman Reigns would have won the WWE Championship by defeating Brock Lesnar at WrestleMania 31.
WWE is the reason Reigns isn't WWE Champion today, whether they realize it or not.
Daniel Bryan was (and probably will be once he returns) the most over wrestler in a very long time. He returned shortly before the Royal Rumble. Many fans assumed he would win the Royal Rumble. There was one problem...
WWE, more specifically Vince McMahon, did not want Daniel Bryan to succeed, and they still don't. That's been well documented, and it was not just a storyline.
When Daniel Bryan was eliminated, fans got pissed, shocked, and even embarrased (at WWE's stupidity) all at the same time.
Can you blame them? Bryan was the likeable underdog who had heart and passion, but WWE didn't want him to succeed.
Reigns was the guy who had everything going for him. He had the look and physical skills. WWE wanted him to succeed.
Who would you cheer for?
That doesn't even mention the terrible booking of the match itself.
Big Show and Kane completely destroyed and eliminated all the fan-favorites in the match, most notably Dean Ambrose and Dolph Ziggler. Roman Reigns was built up as the last hope. No one wants to see a wrestler booked that strong unless you're Brock Lesnar, and he's a former UFC fighter so it's justified.
WWE basically signed Roman Reigns's popularity's death wish.
After the match, WWE was even more desperate in getting Roman Reigns over. They had Reigns's cousin The Rock, who is possibly the most popular wrestler of all time, come down to the ring and endorse Reigns.
Philadelphia booed The Rock and Roman Reigns right out of the Wells Fargo Center.
You might ask, "Why would people boo The Rock? "He is like the bestest sports entertainer ever."
Because Roman Reigns was trying to leech off of his popularity. That's all Reigns had done up to that point - leech off the popularity of more popular wrestlers - mainly The Rock, Seth Rollins, and Dean Ambrose.
Then, WWE had an even worse solution than ever before - Have Roman Reigns leech off the popularity of Daniel Bryan by defeating him clean in the ring and receiving his endorsement after the match.
Add Daniel Bryan to the list of more popular wrestlers Roman Reigns has leeched off of.
Then, the build to WrestleMania 31 was awfully executed.
Brock Lesnar and Paul Heyman rarely showed up, which isn't necessarily Reigns's fault. Now, Reigns was being booked as the underdog, which completely negated all the booking that he received after Seth Rollins turned on The Shield. In a sense, it was yet another example of Reigns feeding off of Daniel Bryan's popularity. On the last Raw before WM31, Reigns and Lesnar played tug of war with the WWE Championship.
Another mistake on WWE's part was not booking Lesnar like a heel. Back then, Brock Lesnar pushed an amputee down a set of stairs. People hated Lesnar for that (kayfabe wise). Think of it like this, why should I boo Brock Lesnar? Lesnar didn't get booed, but Reigns did - right out of Levi's Stadium.
Reigns did put on a good performance at WM31, but it wasn't enough. The Royal Rumble fiasco and everything afterwards were very fresh in peoples' minds.
After 'Mania, Reigns went into a feud with Big Show, which was another attempt at making Reigns look strong. "If Reigns can beat Big Show, he can beat anyone!"
Since then Reigns has teamed with Dean Ambrose several times, leeching off of his popularity.
All of that is why I will NEVER accept Roman Reigns as WWE Champion. I would compare this situation to the old "stain your rug story." Sometimes, you stain your rug. You can get most stains out, but some are permanent. Royal Rumble 2015 and the build to WM31 is a permanent stain and will NEVER go away.
I apologize that this is a pretty long read. I thought it was necessary to fully get my point across.