Closing the resort entirely and doing a major redo all at once is much less costly then a bit-by-bit redo with guests on the property. You can work virtually round the clock,don't need to put up "view" or safety barriers,etc.
From the guests point of view, would you want to spend a year or more planning and saving for your first time special family trip to WDW only to find you have a view of carpenter butt crack every time you look out your window.No matter how they try to hide the work or reduce the noise,your vacation is still a little tainted by them just being there.
The fact that bookings are down just makes the decision to close CBR that much easier. Eventually bookings will increase and they'll have the resorts in tip top shape. I do feel bad for those who were looking forward to staying at CBR and now have to change their plans, but I think the other moderates won't disappoint them.