There's a theory that "rushing them to the bigs" is harmful to development.
In many cases, the players haven't reached physical maturity and so there is also a concern of injury from playing with the fully developed men in a heavy contact league.
Another thing that I've heard is that if your team is still in 'rebuild mode,' the young players could get wrapped up in a losing mentality/culture that is also considered bad for development.
Others say that you can also 'overcook' young players in the farm system.
All this to say that there are many ways to approach development and fanbases are typically unhappy until there are some good results on the ice and then we tend to spend more time enjoying the product instead of languishing over every part of the organization that we feel needs fixed.
Guess where Coyotes fans spend most of their time!