Is this because sport is very different in the U.S., where "winning things" is secondary? With the huge Premier League TV money, even qualifying for the Champions League is no longer as big a deal as it was, as far as the owners are concerned.
Utd are a commercial juggernaut and while they lag behind Barca/Madrid on the pitch, they are miles in front from a marketing/business perspective. That is all that the current power brokers are interested in. People will immediately say "but surely the asset has to perform to be attractive to investors..." - and the answer to that is not necessarily. The Premier League is the most marketable and widely broadcast league in the world and with that comes a premium to any potential investor. Utd can charge through the nose (as can any PL club).
In my opinion its the worst run sporting franchise in the world right now (purely from the sporting perspective) simply because every decision made is from a business perspective. Its set up as a business with an Investment Banker heading up the football operation when no other top club in Europe is set up in that manner. While they pioneer new ways to generate revenue, they operate the football side in a manner that was becoming extinct 15 years ago. We haven't moved on and we've let the competition not only catch us, but run right past and leave us for dust. Chelsea and City are so far in front of Utd in terms of infrastructure its scary.
Its interesting reading the debate on this thread about time being afforded to managers and those opposed to the idea 2-3 year cycles - its been inevitable for years that we would reach this point. Ferguson's mantra of "the manager has to be the most important person at the club" was true for him....but nobody else. We will never see the likes of him again simply because the landscape of everything surrounding football has completely changed i.e. the upbringing of those coming into football (Ferguson was a staunch Union man), the desires of supporters for immediate success, TV, media, marketing.....everything has changed. We as fans are quick to realise the problem with young players nowadays is they get so much so soon, well the same is said for future managers - they are of the same upbringing, same ideals etc. So, the idea that both the club and a large portion of supporters still cling onto the idea of a legacy appointment is futile - its never going to happen in modern football. Whether that's right or wrong or what some of us want is irrelevant - we wont see it again. With that in mind, it puts the club in a position whereby they have to be thinking 2-3 years & get as much success as possible. However, the secret is to have the structure within the club that allows the club to prosper even in the event where the manager (or more accurately "Coach") changes.
All in all, until Utd realise the need to set up the footballing side of the club in the appropriate way to suit modern football, we are not going to see success. Its a sad truth and it hurts as a Utd fan to think we are in this position but simply put: Structure first, Personnel second = Success.