not only do the coaches have much more knowledge/experience when it comes to analyzing all the pertinent data when making personnel decisions, they also have a much larger data set to analyze than we fans do. So you're comparing your molehill to their mountain of data and expressing an opinion based on that.
It's also one thing to say "here's what I would have done" or "here's what I wish they would do". It's quite another to say the coaches are wrong, especially when it comes to personnel decisions. Not saying you're saying that, but plenty have.