Okay, I'll bite again.
My central point: The ad may be okay for Iowa but might further alienate PoC nationally who are on the fence about joining Bernie's cause.
Bernie continues to have problems appealing to PoC nationally. This ad doesn't help.
You originally stated that because the ad has several minorities, there shouldn't be an issue. Problem is there's at most 8 in the foreground; I counted 4. More importantly, the ad goes 18 or 22 seconds showing only white families before they arguably show a PoC. Let me show you my thought process. For eight seconds or so, I give the ad the benefit of the doubt. Nine seconds in, I start waiting for them to show a PoC and don't get one for 10-12 seconds. Then it becomes a counting game. That was honestly my reaction when I first viewed the ad. And thing is, it wasn't just my reaction, but many others from the looks of the discussion in this thread.
You also originally asked if deliberately putting in minorities just to appeal to them would be insulting. Think of a situation where you're planning a family outing and you invite all of your brothers and sisters, but forget one. Billy, your oldest brother reminds you that you forgot Bob, and you ask him, well, wouldn't it be insulting if I invite him now? Of course not, Bob says, it'd be a bigger insult to not invite him! The bigger potential insult is that Sanders' campaign views American families as white, not that they would have to go back and make the ad more inclusive to put aside such an interpretation.
You further stated that minorities were capable of making political decisions without being pandered to. Yes, people of color definitely are. But I'm not talking about what we're willing to stomach. I'm sure progressives are perfectly capable of voting for Hillary Clinton, but we're discussing the ideal, and I think the ideal would be to not share this ad nationally and keep it local to Iowa. Alternatively, if the ad had had 2 PoC in the coffee shop/Mac store scene, I may not have picked up on how white the ad was.
Now, as for why this matters.