Reddit mentions of The Kansas City Athletics: A Baseball History, 1954-1967

Finley was constantly threatening to move the A's all over the country everywhere from Dallas to San Diego to Chicago to Milwaukee. While at the same time, telling the leadership in KC he was not going anywhere. If I remember correctly, the AL commissioner had to force Finley to sign a new lease with KC in 1966 when Charlie tried to back out on a deal with the city. By the time 1967 rolled around, the city, county and state executives just wanted Finley and the A's gone.

Oakland was looking for another revenue stream on top of what the Raiders were already bringing in as a successful franchise at the time. They thought some football fans would also support a baseball team and 81 home games sounded like a great idea. Finley was quoted as saying Oakland-Alameda County Coliseum had, "world class facilities" and, "second to none climate."

I know this does not fully answer your question, but even with all of the current information we have about Charlie Finley, I do not believe anyone truly knows why he moved to Oakland, or understood his way of thinking for many of the things he did.

The Kansas City Athletics: A Baseball History is a pretty great book which gets into far more detail.