This is the short version. Dorell Wright was not in the team’s long term plans. And that’s really what it amounts to.
UPDATE: The only slightly longer version: It appears that the original deal was misreported and the Warriors are receiving vet point guard Jarrett Jack from NOH as part of the deal. Jack is in the last year of his contract and provides some insurance in case Curry goes down. As players go, Jack seems to be in that middle ground around average in so many regards, though he backs up a position where we needed help.
Do not take this the wrong way. For the most part, Dorell played well for the Warriors. Great? No. But certainly better than bad. His "decline" last season was a factor of playing fewer minutes. On a per minute basis, his "numbers" were rather similar and indeed he was a somewhat more efficient scoring in a season where efficiency around the NBA was generally down. His performance relative to the season before seemed to be well within a range of normal variation.
Did Wright's defense seem more lackadaisical, especially towards the end of the season? Sure, but this seemed more symptomatic of a team that halfway through the season was clearly going nowhere, where the players knew this and where putting in more effort could have been counterproductive. Would having him providing more effort have been a plus for a team? Would it have been a plus when a single extra win would have meant sending our draft pick to Utah?
In a fit of irony, if his play cost us even a single win in 2011-2012, Wright's own ‘regression’ probably sealed his fate simply because it allowed management to take Harrison Barnes in the draft. Barnes has yet play a second in an NBA game, and although it’s still entirely possible that Barnes will be a flop, management must feel he presently holds more promise to be something more than an entirely average NBA player. That’s what Dorell was, is, and will probably remain for a few more years. There is nothing wrong with having average players on your roster, but odds of Dorell becoming more than this are vanishingly small. And there is little sense in holding on to average players who play a position that’s relatively easy to fill, where you’ve got other options and want to invest more in one of these options.
Would we have wanted to sign him as a free agent right now at what he’ll earn next year? Really? Of course not. It would have been a meaningless signing that served only to further compromise our cap and tax futures.
The window to trade him without having to take back salary was open, but it would not have stayed open forever. It required a team with cap space willing to take him on. Teams don't tend to have cap space during the season. Waiting for this mythical deal where another team rushes to send a pick our way would mean waiting while teams with cap space used that cap space. There wasn't going to be a better deal and a similar deal was not going to be there before the trade deadline.
UPDATE: It appears that the original deal was misreported and the Warriors are receiving vet point guard Jarrett Jack from NOH as part of the deal. Jack is in the last year of his contract and provides some insurance in case Curry goes down. As players go, Jack seems to be in that middle ground around average in so many regards, though he backs up a position where we needed help.
It's still not a really big deal, but it helps solidify an area of more need while trading out an area with more potential superfluous parts were available.