Timing is definitely odd.
Pretty easy from a Hawks perspective. They desperately wanted to move up last year and couldn't, so when an opportunity arose this year they made the deal. Over the next three years the Hawks have like 10 2nd round DP's, so they wanted to increase the qualitynatbthe cost of some volume.
From a draft perspective they could have a top15/16 and they are hoping that a couple of teams have different players in that tier and the odds of one of their guys falling to 18 is significantly better than falling to 20. Still odd to make the deal now instead of waiting, unless they're trying to move up further.