It was a bridge time, for sure... but Milwaukee isn't as ideal for a downtown setting as many parks. Sure, there are parts of downtown or downtown adjacent that could have been leveled for a park but the 43/94/794 really split up the city in unfortunate ways. Unless they were able to cram a park into the absurd footprint a la Target Field, getting a park close to an enviable downtown spot without tearing down historical neighborhoods is hard.
Kansas City is kinda the same way. If not for Kauffman being so great, KC would have to face some hard questions about how to place a park in a miniscule downtown area surrounded by stupid freeways.
I'll save everyone here a rant on how destructive American freeways were to downtown cities, all of which was completely intentional and short-sighted.