Well, he said he wanted him on board. Not sure what diplomacy buys him.
I would think the reason is Cherington, who very likely knew Dombrowski professionally, figured he would be unable to work with him, either because they had drastically different philosphies or he figured DD to be a micromanager, or possibly even because DD was an insufferable human being.
But bear in mind, Cherington worked under Lucchino, who carries an (undeserved?) reputation as a micromanager himself, and under Henry, who hamstrung his ability to spend anything his first year as well...