I've been beating this point like a dead horse, but I can't resist... NBA front offices and head coaches are really into the idea of players who can defend the pick and roll and guard multiple positions. If you can't do that, teams can easily scheme you out of being productive when you're on defense. That's the problem with players such as Lopez. He's not even good one-on-one guarding back-to-the-basket bigs, and he's not shot blocker even though he's tall. Meanwhile he's heavy-footed and slow going out in space.
If he was Kevin McHale on offense, then that'd be something. But he's good, not great on that end of the floor.
In other words: the Nets are cooked for a long time.