We are already getting a Chewie prequel. Its the Han Solo movie.
And I wouldnt call it laziness. Its a sensible business decision. There has been a demand from the fanbase for an Obi-Wan film. IDK how high that demand actually is but its been something thats been repeatedly asked about by fans, bloggers, and interviewers. Ewan's Obi-wan is liked, and Ewan has repeatedly expressed his desire to return. It makes financial sense that theyd want to do an Obi-Wan film.
Also, lets keep things in perspective. This will be the third anthology film set in the OT era. It will be Disney's 6th star wars film. By the time we get to 2020 we will have 3 films set in the Republic era, 6 films set in the Imperial Era and 3 in the First Order era. We will have 6 films featuring Leia (She was cameo in one of those.), 5 or 6 films featuring Luke, and 5 films featuring Han. This will be the 7th film featuring Obi-Wan and 2 of those films he was little more than a cameo. All those films introduce new characters, new places, new ideas.
This is very similar to how Disney and Marvel have handled the MCU. They produce films all set close to the same era that all link closely together. With a core set of characters that are constant throughout the films and new characters and elements are introduced throughout those films. The only films thats really branched out and did something really different is the two GOTG films, but even they link back to the rest of the films. And all those films are working together towards a goal. Theyve mentioned they might try something really different with Phase 4 after Avengers 4.
So why is it bad when Disney and Lucasfilm do pretty much the same with the star wars franchise? Why do people automatically ***** about the idea of a film set in the Imperial era? Why is there this dumb demand put on Lucasfilm that they do something completely out of left field right away?