It´s not better basketball that you´re selling them, it´s a better idea. George Hill has never drawn in crowds, and whatever Z-Bo did for Memphis is long gone now, nobody is ever going to say, “hey, let´s go watch the Kings and whatever George Hill is up to”, but you´re telling your fan base, specially after trading DMC, that you´ll be trying every night, that you´ll put up a fight, and that they´ll be getting a decent show for their money.
Because your fan base could be walking away, loyalty or no loyalty, and not necessarily to benefit some other in-town franchise. NBA tickets don´t come cheap, and, in the era of Netflix and NBA League Pass, it doesn´t take a lot to make a family say “stuff it, we´re making popcorn and watching the -insert team & sport here- on TV, with 4 or 5 game nights like this we save, we can go to -insert suitable family holiday destination here- for the Easter Holidays”. There are some people, including myself, for whom going to actually watch their team in their grounds is special, but not everybody, not even the majority, are like that, and they will as soon walk away as stay.
Even if you say you´re keeping your Kings season pass to watch GSW or SA or the Rockets when they come to town, watching any of those is no fun if they don´t have anyone trying hard to stop them. It´s a product that you´re selling, not a win percentage, and products are, specially entertainment products, much more about expectation than reality.
Also, by the same token above, George Hill and (old) Z-Bo aren´t going to massively improve your win %, either. As value-over-replacement, they can´t be worth much more than 5 wins, and that moves you down maybe one spot in the draft, big deal. If you overdid it, and, come the All-Star Break, you are indeed much better than you thought, you either trade Hill to one of the top-4 seeds in either conference for a future pick (and whatever veteran is not working for them or is injured, to make the salaries work), or, as Tyler says in the other reply, you just bench them and ride with Buddy and Willie, no sweat.