What killed the Braves in Milwaukee? Inept marketing. You mention the Celtics.
Marketing the NBA to Boston was a tough task -- in the 1960s, Red Auerbach came up with creative ways to promote the Celtics - particularly offering discount tickets through hamburger joints (Howdy Beefburger) and also inviting high school teams to play before the Celtics games. There were also promos with NBA doubleheaders - yeah, you could see TWO NBA games - almost half the league - for two bucks. And the Globetrotters, and a Globie-type act called the Fabulous Magicians also would play before Celtics games.
Then UHF television came along - and many away games were broadcast on those stations - again, promotion. This is what killed the Braves in Milwaukee - as I said above, Lou Perini would not allow ANY television of any Braves games for too long of a period, and after the craze of a new, contending team wore off, he found out that he had lost the next generation of Milwaukee baseball fans.
To be fair, in the 1950s, sports team owners didn't know whether to embrace television, or fear it. Early NFL telecasts - particularly experiments with the Los Angeles Rams and home game telecasts in the early 1950s were blamed for laggard attendance thus the NFL "no home game" blackout policy went into effect. It carried over into other sports, including the NBA, NHL, and MLB (not as stringent). Any time a new technology comes along -- some people fear it, some look at it cautiously, some embrace it.
Example = fifteen years ago, radio people I knew scoffed at online streaming, probably out of fear. Now, many are "independent consultants" (read = "no job") and the entire radio business is teetering. but....back to TV...
It wasn't until the mid-1960s that they finally understood how they could use TV to their advantage. Thank Vince McMahon, Sr., and his wrestling show promotions, to teach them. His then "World Wide Wrestling Federation" was a regional operation, he syndicated his product and it got people to come out and pay to see it. All sports finally figured out - if you televise at least PART of your schedule, people might want to come out and buy tickets to see your product.