And, BTW, your knowledge of geography and baseball history could stand a little improvement. When the Dodgers and Giants moved to the West Coast, Kansas City, not St. Louis, was the farthest west city in the major leagues. And no, Milwaukee was hardly a "frontier" in the 1950s, since it is only 90 miles or so from Chicago, which had had major league baseball since the beginning of the sport..
After the 1960 census Milwaukee was one of the ten or twelve largest cities in the U.S.
Just looked it up. It was 15th in population in 1960 with a population of roughly 735,000. Among NL cities, it ranked 5th of eight in population, trailing Chicago, Los Angeles, Philadelphia, and St. Louis, and exceeding San Francisco, Pittsburgh, and Cincinnati. I don't have the metro area figures on hand.
After the 2000 census, it doesn't even show up among the top 20 and I believe it had fallen to #25.
That's a very interesting table. Buffalo was the 8th-largest city in the U.S. in 1900, and was ranked among the top 20 as recently as 1960. And yet it's never had a big-league baseball team since the Bisons folded in the 1880s.
Regardless of whether St. Louis or Kansas City was the westernmost team before 1958, the point is that there was a whole lot of real estate in the western U.S. with no major league teams back then before 1958. No Houston (#7 among U.S. cities in 1960), no Dallas (#14), no Phoenix, no Minneapolis/St. Paul, no Seattle, no Denver, etc. In fact, there were no teams at all in the Mountain Time Zone when the Dodgers and Giants moved out to California.
It's worth noting that even to this day, Milwaukee only has two big-league sports teams (the Brewers and Bucks). It simply isn't much of a big-league sports city, in terms of either size or a long tradition (like Cincinnati has). In that respect it's very similar to Pittsburgh: a city in decline that struggles to hold onto its professional sports franchises as other cities become better markets.