One practical reason for this is that the Democrats don't benefit from allying themselves with gun control activists. That would alienate them further from the Blue districts that elected Trump. It's one of those issues on which you tread lightly to get elected in this country. Obama was soft on gun control in his Presidential campaigns.
Another reason is that, yeesh, David Hogg is 18 years old and has more than a touch of narcissism. It seems like only a matter of time before he ####s up big. Maybe he gets recorded saying "fag". Or gets accused of some sexual misconduct, whether it's true or not. All it takes is one wrong move for that ship to sink. And young guys entering college often make a lot of wrong moves.
Seriously, he's going to be Joe the Plumber in a year. All of the controversies about him are stupid.
Laura Ingraham should not have abolished for criticizing him.
And all of that this fruitcake above needs is a little patience.