The problem is that the Spurs want to find a Bowen's replacement for the cheap or with a second round pick. Finding a new Bowen in that way isn't going to happen.

But there are many good wing defensive players. Various are also all-nba players, those go for max contracts only. The best defensive specialists in their prime command around MLE long term contracts.
The problem is the Spurs want to find a Bowen replacement with only one guy, while simultaneously stockpiling guys who specialize in the lowest percentage shots that result in the highest percentage of long rebounds.