THE RATIONALE: Memphis is probably inclined to hold onto Thabeet for a couple years and see how he develops. Trading him would be admitting they drafted a bust. So, they won't give him up for nothing.
Prince, Summers and Jaric are expiring contracts (Summers is included to maintian roster size) so essentially this is Thabeet for the Pistons first round pick. From the Pistons perspective, there probably aren't any shot-blocking big men available in the draft this year, so rather than draft yet another wing player... From Memphis's perspective, they have Gasol and Haddadi to back him up so maybe they draft a more pressing need (power forward?).