The only thing I can think is that it was a last-ditch attempt to save the season. They actually didn't save any money (what, $200K?) and all players involved are going to be free agents at the end of the season.
If you want to take a bright-side look as a Kings fan, at least you can say that with Wall done, their efforts to save the season are basically doomed. At this point, their best bet would seem to be to get under the tax level in order to stop hemorrhaging money while they figure out how to build a competing team while stuck with the four years and $177M left on Wall's deal. Tanking for a good lotto pick, starting ASAP, would *seem* to be the right move.
And we are, best as I can tell, the only team that can get them under the tax threshold - certainly the only team that can do that without serious machinations (like trying to make five trades each saving $2M). But I have to say that our cap space comes at a price - that price's name is Otto Porter.
I know Otto is a steep price, but look at it this way: The Wizards are going to be in the tax this year, barring a change. They were in the tax last year. And being in the tax three out of four years puts you in the even-worse "repeater" level of the tax. But how do they avoid being in the tax next year when they're paying $108M for four players, one of them recovering from surgery (Wall) and another not really any good (Mahinmi)? They don't. So it's Repeater Time without making a big move. Now, I suppose they could try dumping Mahinmi for an expiring contract and suffer the tax this year while trying to slip under it next year, but nobody really wants to pay Mahinmi $15.5M next year. What do they have to offer? This year's draft pick? Well, that might not be enough incentive for another team to eat $15.5M next year - and if it is, then how in the world do the Wizards hope to start filling out their roster without that draft pick?
But we can fix this for them. We take Porter and Mahinmi, and we send them the expirings of ZBo, Kosta, and BMac and an actual asset in Justin Jackson. I'd love to do this deal without sending Jackson, but 1) he'd lose all his time with Porter in town, 2) the Wizards will still insist on getting *something* of value back, and 3) if I've got it right we really need to include JJ to get the money to work. Is this an overpay for Porter? In cash terms, probably. You would have to consider the Mahinmi contract part of Porter's money, so (assuming we did this at game 41, for easy pro-rating) we'd be paying about $92M for 2.5 years of Porter, almost $37M per year. That's a lot, but right now we can *afford* it, and we don't have a lot of options to improve SF, certainly not to the extent Porter would, otherwise. Imagine adding Porter now, and with a year to gel, a lineup of Fox/Hield/Porter/Bagley/WCS(re-signed) with Bogdan/Giles/Bjelica/Shumpert(re-signed) off the bench could look VERY SCARY. And it's affordable. In exchange, the Wizards get out of the tax this year, they start the tank immediately, improving their pick, they gain a rotation piece in JJ, and they get elbow room to start rebuilding around a two-star lineup in Wall/Beal. Furthermore, it's kind of insurance against having to pay Porter (and Mahinmi) all that money over the next two years if Wall doesn't bounce back to form. I know it's hard for them to pack off a near-star player and not get much return, but the financials and the reboot it offers are not exactly available anywhere else. The Wiz might decide to just ride the franchise into the ground rather than ship off Porter for a bag of donuts, but it's probably a bad call. If you're in a hole and someone offers to take away your diamond-crusted shovel for free, maybe you ought to give it to them if only to stop digging.
Now, a trade like the one I outlined actually would have to take place in two parts to get under the CBA rules. First we would send ZBo and Ben for Porter, which would allow us to slip Porter into our cap space. Then as a second deal we would send Kosta and JJ for Mahinmi, which would be a legal salary match. Lumped together the deal wouldn't be legal because we'd be taking too much salary back, but if you split it apart into two parts correctly, it works.