Lou Williams is a solid player, but he's not part of the Lakers future...so his salary is a sunk cost. Also, they would rather give William's minutes and experience to the young guys (correct move). So to me the Williams for Brewer part of the deal cancels out from the Lakers perspective.
Could they have traded him for cap relief? Maybe, but that might not have been a goal. If I were the Lakers acquiring a first rounder would be the course I take.
ETA: Seems  like the options are unless something else is reported but....
(1) take back salary, get a 1st
(2) cap relief, no draft pick
Obviously, getting a 2nd and cap relief would be best, but judging from what they accepted it looks like it wasn't offered.