This is me reaching.
There are some teams who just aren't going to be winning any time soon. When you get them, there isn't much point in investing in an expensive coach. Firstly, it will be hard to get them to sign, because the team is $#!T, and secondly, you will be paying a lot for a lottery team that wins more games than you really want it to, since it's only going to hurt your draft position and make the rebuilding process more difficult.
Enter guys like Wittman, or rookie coaches. They won't charge as much as a good coach, and they will take what ever job they can get because they have no experience or no results to show. That is why Sac-town likely brought in Smart. Why the Hornets got Monty Williams. Why Charlotte has Mike Dunlap. Why toronto has Dwayne Casey. Why Orlando has Jaques Vaughn. And when the team is good, it's easy to fire them, because they have a $#!T record so you are justified, and they aren't making much. And rookie coaches will always be willing to take these jobs with the hopes they can overachieve and earn a rep to get a big pay day and a better gig (see Doc Rivers in Orlando and likely Mark Jackson in Goldenstate).
And then you get other teams like Detroit and Phoenix who don't expect much and get a head coach with a spotty track record like Franky and Gentry.
The thing is, when these coaches do bad, there isn't much point in firing them mid-season because these teams aren't in the playoff hunt, and likely don't want to be, so waiting until the offseason makes more sense. You get better draft positioning and you team is more attactive to prospective coaches.
Who ever coach a playoff potential team that goes on a losing streak next
whoever coaches the wizards