There is no inherent reason. When he first started they wouldn't stop ranting about 'mister Saturday'. Last couple of years He has been in the publicity doldrums because, prior to this year he was alongside an established superstar, and this year the Max vs Mac story is dominant. Also he hasn't been in a serious championship fight yet. His position falls through the cracks a little.
If he becomes the main challenger (which he clearly has the ability to be), and especially if he wins one, he will be another star and centre of attention.
Talking about 'oh he loves himself too much' or 'he isn't fan friendly' or 'he is a bland posh English person' is all nonsense to justify why your own favs get the media time. Max isn't anyone-friendly. Lando is a strange quiet person with no discernable personality. Lewis is a bit of a nutter and self-centered as a gyroscope. Michael was an odd person in cowboy boots. Senna was arrogant to the point of thinking himself god-appointed. No-one cares about any of it if they win and win plenty.