Luck is a part of this game, but choosing a time to rebuild has nothing to do with luck. Ofcourse BB can not be constant throughout all seasons. There will be better/worse times to do certain things. No need to complain.
I think that all here agree that the valkue of a player depends a lot from their age
If you see that your team is going nowhere,and you are start to think to rebuild,you can't lose so many season waiting that the market price will rise again,befcause the value of your older player became less and less while the season pass.
Choosing the right time to rebuild their own team often depends from the age of your team,more than from other factors