People are sick of Roman being da face of the company, unfavorably maineventing all those manias. He's obviously was booked the top guy but rarely held the title. A weird bit of booking.
All you need is to look at the context of all those title reigns.
His first title reign he lost after being cashed into by Sheamus, won it back pretty much immediately after, only lost it after having to put it on the line against 29 other people, only to win it back in the main event of Wrestlemania. Just because he wasn't the champion the whole way doesn't mean he wasn't the top guy the whole time.
He only lost the title to Rollins because he got hit by the wellness policy test, then the title went to Ambrose to be the top title on Smackdown. Don't worry about Roman since he now has the UC to fight for.
Roman was still in his depush phase so he was in the midcard for a while, and they were super interested in Balor and Rollins at the time. This was the only period where I felt like they didn't have much plans for Reigns, until mania season came along and suddenly out of no where Reigns vs Taker was booked and main evented Mania, signalling the restart of his push.
From then on, Vince was dead set on having Roman be the one to beat Brock for the title so cue Brock destroying everyone for a year and a half until Roman comes in and unseats Brock. Only for the cancer to show up forcing him to relinquish it.
He was always primed for the world title for most of the time since his first world title win. The only time he ever lost it fairly was to Seth, and Seth was returning hot at the time while Roman got busted by the wellness policy. Had that not happened and had Roman had not gotten cancer, I'd guess you'd see he'd be having much longer title reigns,