The four elementary schools being replaced were built in 1975, 1980, 1985 and 1987. Not young but not old. Austin's Bowie HS was built in 1987 and the current Austin High was built in 1975, about the same time span.
Austin ISD, by comparison, is just now replacing Travis High School, which was built in 1952, leaving rodent-rich McCallum, also class of '52, as the oldest high school building in town.
As part of that 2019 bond, Keller ISD built four indoor air-conditioned football practice facilities, one at each high school, for a cost of $48 million. By today's standards that is actually a pretty good price for that kind of building.
I've been paying attention to the Austin ISD bonds since they started with the big bonds in 2017. Old elementary schools get completely replaced. At the middle and especially at the high school level, there is a lot of focus on improving athletic facilities and not as much focus on academic areas. This is not exclusive to Austin ISD, there is an athletics arms war going on all around the state.