A reboot doesn't necessarily mean new cast. That would be a remake.

Making a new season after a hiatus is a way to reboot the series and get it going again. It's happened before with X files.

Timeline has its flaws, but it's not an awful movie. I like how time travel wasn't used primarily as a tool to avert disaster. Interestingly, it helped reveal a certain character's future in an unexpected way.

It does make you wonder how much of this recasting is pandering. My point being, there is already a viable character in DC for this role. Luke Fox. Ex military, intelligent, very capable, moral and takes on the mantle of "Batwing". Why has the opportunity to explore this story been ed over in favour of completely rewriting the original story of Batman?