Pilots and Royals
It was also demographics, the long term abilities of Buffalo supporting a team did not look too good in 1969, the city was losing population hand over fist and baseball was looking for growing cities such as Atlanta, Toronto and San Diego. Of course putting a team in Montreal didn't make a lot of sense either, the city had no stadium, and no ownership group in place, it would have made more sense to put the team in Milwaukee where both of those problems were already addressed, and was a proven MLB town.
If they would have put that fourth team in Milwaukee, where do the Pilots move then? Dallas? Buffalo?
Now the 1969 expansion draft is likely not to happen in 1969, MLB was wanting to do it in 1971/1972 when Senator Symington got involved and said theres no way in hell he will allow KC to wait that long, so it was bumped up a couple of years. The rushed expansion cost Seattle, the Pilots, and nearly cost San Diego the Padres.
If Symington wanted a team for KC so bad, they should have just had the Royals and Montreal join MLB in 69, and then the Pilots and Padres in 71. Then, maybe the Pilots stay in Seattle, and, in 77, Toronto still gets a team, but Denver comes in with them instead, and has Marvin Lewis as the owner. They would have called them the Bears. As for Milwaukee, maybe they get the Senators instead of Dallas, who might have had to wait until the late 80's or 91 to get a team.