One possible factor in Darius Morris's decision to enter the draft is this year's change in the deadline for withdrawing from the draft. Prior to this year, that deadline was set at ten days before the draft, which is held in late June. According to this Sporting News article, the NCAA changed this year's date to May 8 at the behest of coaches from the ACC:
Coaches from the Atlantic Coast Conference complained this was causing problems with knowing what players they would have on their rosters for the following season. They successfully pushed for a rule change that instituted an NCAA withdrawal date for early May, giving college underclassmen almost no useful time to establish their value to NBA teams.
This unilateral deadline imposed by the NCAA has been widely criticized by members of the basketball industry, as it is clearly a self-serving rule intended to protect the NCAA's interests by severely restricting players' ability to explore their professional options.
This deadline has put a significant amount of pressure on NBA teams to evaluate a huge group of players in a short and highly inconvenient period of time, then disperse valuable information about those players that could influence whether or not to keep their name in the draft. This is an exercise most NBA teams were not happy to participate in last year.
With the way the rules are currently set up, players have a window of only 10 days to decide whether or not to withdraw – from the time the early-entry list is officially released to teams (typically four days after the deadline, April 28) to the date the NCAA has legislated underclassmen must declare their intentions in writing to the school's Director of Athletics, May 8.
Since the NCAA also restricts student athletes from missing class to “try out for a professional team,” players are essentially relegated to the weekends of April 29 and May 6 (the same date as the Euroleague Final Four) to attend NBA workouts and get an accurate reflection of their draft stock – something that is virtually impossible due to the logistics involved.
The Nets will host a mass workout for draft prospects the weekend of May 7-8 as a way of helping college underclassmen get around an NCAA rule requiring a go or no go decision by that weekend. Although only underclassmen are [affected] by the rule, the workout at PNY Center is open to all [i.e., seniors and international players may also attend].
Also worth noting from that article: "Unlike other workouts in the past, this one will include 5-on-5 scrimmages as well as the usual measurements and interviews." The rules for these workouts had previously held that no more than six players could be on the court at one time. All 30 NBA teams are expected to be there. (Also from netsdaily.com, this page provides a good rundown of NBA draft-related deadlines and events--just ignore the Nets-specific info.)
Given the speculation by some that Morris is simply going through this process as an exercise to better prepare himself for next year, what better way to do that than to participate in this first-of-its-kind mass workout/combine? That's the positive the way to look at this. On the negative side (from the selfish point of view of a Michigan fan, that is), participating in this type of workout certainly provides an opportunity for him to improve on the evaluation he's already received from the NBA. Either way, if he does participate he'll need to make a very quick decision on whether or not to withdraw his name.
Additional note: USA Today story from yesterday says that 44 players will participate in the May 7-8 workout but doesn't name them. The story also says the withdrawal date may be moved up even more next year:
Underclassmen could have even less time to make their decision next year. An NCAA proposal, which will be voted on April 28, "would require student-athletes interested in 'testing the waters' of the NBA draft to remove their name from consideration before the first day of the Spring National Letter of Intent signing period."
This year, the first day of the spring signing period was April 13, about a week after the NCAA men's championship game.
Story has a long quote from the ACC giving their rationale for the proposed change.