I think you're misunderstanding who has fucked around, and who is finding out.
The "uncommitted delegates" may not be the actual people who have heckled Harris at her campaign rallies or who are blocking delegates at the Convention or who have repeatedly promised to turn Chicago into a replay of 1968. But they are closely aligned with those people. And the fact that those actual people have actually done those things tells me either (1) the uncommitted delegates are complicit, or (2) the uncommitted delegates are not leaders in the movement and have no sway or credibility.
Either way, there is no benefit to giving them airtime.
There is, however, a huge detriment. They're unpredictable. They could completely fuck things up because you absolutely cannot guarantee that these people aren't going to go rogue. They're also unpopular. Their position is not supported by the vast majority of Americans. So why would you possibly give valuable airtime to a group that, on their best day, are going to get up there and say shit that most Americans don't really support?
Finally, there is a big benefit to excluding them. It sends a message. It's general deterrence. The days of the Democratic Party playing nice are over. This is back to LBJ-style politics. And that style of politics is damned effective. Don't think you can fuck with us and we'll still give you what you want. You may have gotten away with that shit under Biden and under Obama. But fuck that noise. We're keeping the receipts. You can't trot around calling the President "Genocide Joe" and then think you're getting any time to talk at Joe's going-away party. You can't heckle Kamala Harris from the crowd and then think you're going to get to talk on the night she accepts our nomination.
And you know what? Telling these people to "fuck off" shows strength. And strength is popular.
It may lose Harris like five votes in Michigan. Guess what--she'll still win Michigan by about six points. But it'll also gain her votes in Pennsylvania, Wisconsin, Georgia, Arizona, North Carolina, and Ohio.
Oh, yeah--the Democrats are going to find out all right. They're going to find out that telling people to fuck off in a very public fashion is often the popular political move.