Baylor has been hitting coach for the Diamondbacks since 2011, having previously had the same role with the Brewers, Cardinals, Braves, Mariners and Rockies, at various times since 1990, as well as spells managing for the Rockies and the Cubs. With the Angels making #7, maybe he's attempting to be the first person to be the hitting coach for all 30 teams.
I believe Don and his wife live in La Qunta, California, so perhaps that explains the reason for the lateral move, as he'll be closer to home, with Angels Stadium about 25 miles away. Alterantively, Piecoro notes he'll be under GM Jerry DiPoto, who played for Baylor when he was manager of the Colorado Rockies from 1993-98, so perhaps there's some kind of personal connection there.
Assuming this is an accurate report, it leaves the Diamondbacks in need of three coaches for next season, with vacancies also at pitching and first-base. For the first time this year, there was an assistant hitting coach, in Turner Ward, so it's possible he may be moved up to replace Baylor, or the team may decide to look for an external candidate to fill the position instead.
Still, we'll always have this, Baylor's reaction to a Wily Mo Pena home-run at Comerica Park, in June 2011