A's have made the playoffs 11 times since 2000. They've been a competitive franchise for the most part, so you can't blame the on field product.
Oakland Alameda Coliseum was outdated in the 80s and every effort to replace it has been stymied. I went to a Raiders game in 2012 and an A's game in 2014 and the in stadium experience was atrocious and this was damn near 10 years ago. Can't imagine what it's like now. Other than some exceptions (Fenway Park, Dodger Stadium, Lambeau Field, Wrigley Field) playing in a outdated stadium put the A's in a competitive and economic disadvantage.
If the city of Oakland wanted to keep their teams, they would have made the investment like every city has to do. Libby Schaaf and Jean Quan weren't interested in even trying, so here we are.
Sucks for the fans, but that's business for you,