The entire British media has been obsessed with United ever since Busby. Even when they were shite the last time in the 70s and 80s. All Sky did was a Trump-esque appropriation of that obsession and ballooned it into their own personal commercial behemoth.
I'd hardly say United's noisiest supporters constitute a "large" section of the fanbase.
Although it was before my time, I always thought it was the Munich Air disaster that put Man United into the public consciousness more than anything else. From what I've been told by people older than myself, and what I've read and heard over the years, football and the world in general was different back then. There wasn't the kind of tribal hatreds we see today and, quite rightly in my opinion, the whole country got behind United after the appalling disaster at Munich. Apparently, many, many people vowed to follow the club from then on. After what happened to the club/team, it's no wonder that so many people had deep sympathy for them and developed an affinity for them which endured long after. Coming back from that terrible tragedy to win the European Cup in '68 was remarkable, and cemented them into the public consciousness permanently.
I don't think any right-minded people would have resented the attention placed upon them back in those days. Where resentment did finally set in was in the 70s and 80s when United were an ailing, rudderless shambles. Relegated by the club then known as Manchester City on their own patch in '74. At best they were a plucky cup side, but mostly they were an absolute joke. A laughing stock, yet still full of arrogance. While teams like Liverpool were sweeping all before them at home and abroad, those serial losers and also-rans grabbed the headlines. Clubs like Forest did amazing things, yet United got unwarranted headlines. Everton bagged two titles, and although it was a third rate (now defunct) trophy at the time, they also won a European trophy. An FA Cup too, yet the shambolic Man United would still get the headlines from a sycophantic and fawning media. The media would built them up and declare what they were going to do ... whilst the clubs that were actually doing great things were getting overlooked in the recognition and headlines department. United and their whole media machine were just the gobby loudmouths who amounted to little of substance back then. Think Gallagher brothers today.
Luckily for United, Ferguson arrived on the scene to eventually instill some substance into what had become the myth. They got it right just as Sky were hijacking the game. Hype, bullshit and bling. They were made for each other. The hype around United went into overdrive. Much of the headlines were actually deserved through the Ferguson era, but a lot of it was also pretty sickly. It's a bit like how the press think everyone wants to hear and see what Katie Price is doing, so they will publicise every tiny detail as though it was an earth-shattering story. Facts are, with United and Price, the only people who give a shit are their actual fans. For the rest, it's a major turn-off.
These days it's actually funny seeing them desperately trying to show they remain somehow relevant when their biggest rivals are European Champions for the 6th time, and their Abu Dhabi neighbours are busy purchasing the domestic silverware. The headlines they get are looking all the more silly too, usually centering on some immature antics of their 'star' players. Facts are, there isn't really much to report on at OT anymore other than their decline. Their headlines make useful wrapping for your fish and chips, but that's about it.