Why would Disney make such strange decisions with this franchise?
I suspect it's related to one of three things:
Number one IP. Disney wanted to own the intellectual property related to Star Wars. This means disposing of the existing IP and replacing it with their own. JJ Abrams has a history of doing things like this if you look at Star Trek.
Number two avoiding payments to George Lucas. This is sort of related to the first point. George may have had a deal where Disney had to pay him royalties if they make use of original characters. Disney may have decided to develop their own characters to avoid making additional payments to Lucas.
Number three inability to execute. Sometimes the obvious answer is the simplest. Kathleen Kennedy and Lucasfilm have no idea what they're doing.