I also was a little puzzled by this trade, then impressed when I watched Zerpa in the WBC, and finally disappointed when he got injured.
I did see both Mears and Collins regress in the second half of last year - so that probably played into the trade.
More importantly, the Brewers had a glut of young pitchers and outfielders playing great in the minors - so I expect that was a primary reason the trade was made.