The Lakers didn't give up on him, the Lakers used him to dump salary to create cap space. And it isn't like they didn't make great use of the draft pick they got from the Nets.
As a recap, the trade was
Russell, Mozgov
for
Lopez, 1st (which they used on Kuzma)
Mozgov is still under contract so he would have been a huge detriment in the Lakers free agency the last 2 summers.