The PT was all about Anakin's fall to the dark side which occurred in the time of the Clone Wars. A conflict that was alluded to in the OT and we wanted to know more. TCW became the vehicle to give us what we wanted, expanding all that was good about the prequels and changing/improving wherever it could. Anakin became likeable and his relationship with Obi Wan became the brotherly friendship that old Ben talked about.
Rebels, much like the anthology movies is just filling in gaps where there was nothing going on of interest. Since I was a kid, I've always wondered about the clone wars and all the other Jedi (more so than Vader's beginnings), never cared how the DS plans were stolen or how the rebellion was formed.