I think there's an underlying method to the madness here.
The Brewers currently have four good pitchers on the 60-day IL that are likely to/hopefully come back during the season - Ross, Williams, Hall, Bukaskas. When those guys come off of the 60-day IL, somebody is going to have to be DFA'd.
There is a point where you call up too many prospects due to guys going on the 60-day IL, because at some point you have to take guys off of the 40-man roster when those players come back.
Easy to DFA guys such as Keuchel, Hernandez, Meeker, White, etc., because if they get claimed you aren't going to lose much if anything from your organization. But when those guys start coming back from the 60-day IL and you have to DFA guys you traded assets for (Taylor Clarke, Chad Patrick) or potentially a prospect (Carlos Rodriguez) who could easily get claimed due to a roster crunch, that's not good either.
I just don't think they can add to the 40-man anyone else who is valuable to the org because at some point they will have to DFA someone valuable when Williams, Ross, Hall, and (possibly) Bukaskas come back.