It seems to be a big problem with Mist and Geth. The software is still in the beta stage so there's a lot of work to do.
Last year when I playing with Mist, it took a long time, but it at least completed. Now, it just doesn't get finished. Even the developers seem to acknowledge the issue.
Mist and Geth are garbage and in need of some serious work. It's a black eye for Ethereum to not have a functioning wallet associated with it's main development.