In those 15 years it's been primarily worn by a collection of run of the mill players.
The no 7 shirt was not a thing in the 90s.
It seems to have become one due to the Cantona to Beckham (who only wore 7 because he played on the right of midfield and that was the standard practice) to Ronaldo chain.
When I say 15 years ago, I mean that's the first time anyone started mentioning it and, subsequently, no player who wore it after Ronaldo left was in anyway special.
It's not an institution. It's a meaningless rewriting of the past to create a significance about a coincidence that meant nothing at all at the time that the actually great players who wore the number were actually wearing it.
No-one discussed the significance of the number 7 shirt as Beckham or Cantona wore it.
Yeah, the chain Cantona->Beckham->Ronaldo solidified it.
Disagree with the bolded parts.
Beckham is the one that made the number cool and "majestic" really. Football fans are influenced by him a lot. He is special and a huge football icon. Ronaldo is similarly like that and had the same impacts continue making it special. Since Becks in early 2000s, people make a big deal out of it even attributing #7 wrongly with Best, his number is more #11.
That said, #7 is no doubt special in our history and current's football since late 1990s onwards, seeing how many of our best players arguably wear the shirt. United fans, the players themselves and even football fans in general felt fond of the numbers, so we can't ignore it's implications and big significance right now. Not just our fans, but even non-fans are affected by our #7's players influences.
Steve Coppell
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Bryan Robson
Eric Cantona
David Beckham
Cristiano Ronaldo
Those are players who wear the number with pride -- Cantona maybe don't care much about numbers, Becks initially prefer #10 and made the #7 a lot more special ironically, CR doesn't really care but since wearing it, he is fond of the number, Robson definitely like the #7 number and many older United fans adored the #7 Coppell. The rest that come after them don't see it as important nor influential.
Owen
Valencia
Di Maria
Depay
Sanchez
Fans want to be like their #7 heroes, by wearing the same number and seeing it as a sacred number.