Let me count the ways.
1. He is a league average producer offensively, his supposed strong suit.
2. He has already played his Age 30 season.
3. He duplicates what the Hawks already have in Jamal Crawford.
Salmons only seems appealing because most people assume, because they have only heard his name in the last couple of years, that he is somehow a young player. Obviously, considering he is older than Joe Johnson, that is not the case.
His prominence in Atlanta stems from the (6) games he played against the Hawks in the regular season, upon which he tossed down his second best PPG vs any opponent played more than once (21.3). Three of his top five high scoring games of the year came against Atlanta, 32, 32, and 28, all within a tidy six week stretch of games coming down towards the end of the season when the Bucks could not be stopped. Lusting after players because they played well against your own team is called "Bobby Cox Syndrome."
The cost of bringing in a player who is, at best, at the end of his prime, in which he is still only a league average producer, is a waste of what we know to be limited resources.
Moving Crawford into the starting role at shooting guard and drafting a player to replace Johnson in the rotation would be a more cost effective move. Shoot, chasing down this guy would be much better use of funds than chasing down a thirty something year old "scorer". The Hawks could then gameplan on what to do with Johnson's and Crawford's salary slots at the end of next season if they can't find a decent sign/trade partner for Johnson.
That way they can target someone of plus value who will peak with Al Horford and Josh Smith and isn't a desperate "bargain" (read: cheap) signing to keep up with 50+ wins and likely end up producing less than expected to the point where you wonder where the bargain went.
Pass. Pass. Pass.