Your account is true for Maris, but not for Jackson. Reggie was, indeed, a Kansas City A that followed the club to Oakland where he won Worlds Championships in the 1970s. Charlie Finley dismantled his team soon afterwards and traded Jackson to the Baltimore Orioles. When Jackson’s contract expired, he was granted free agency (something not available to Maris) and signed with George Steinbrenner and the Yankees that winter.
But Oakland was not that much bigger of an MLB market than Kansas City at the time, particularly when you consider that it had to be shared with the Giants across the bay.
The great dynasty team of the 1970s got too expensive and suffered the same fate as the great Philadelphia A's dynasty teams of the late 20s/early 30s and early teens.
One of the best A's teams ever fielded was the 1927 version. I think they had something like 8 hall of fame players on the roster. Nobody much remembers them because they came in second place after what was arguably the greatest Yankees team ever fielded. Even our Pirates fielded one of the best teams ever that year . . . which proceeded to lost to the Yankees in four straight during that World Series.