The difference is that Comcast is a cable television company, and NBC is a TV network with a side of owned/operated TV stations. The Universal studio was acquired (though just barely) when the whole shebang was still under GE, and Universal came along for the ride. (In fact their big contribution was removing the space between "NBC" and "Universal" in the logo.) GE had already figured out how to integrate the two, and how much needed active managing, verses sitting back and letting them manage themselves.
I get what you're saying. I'm just saying that they valued the film libraries of Universal and Warner. At the time the deals were made, those were perceived to be vaults of gold. And as we've discussed here, there's been a sea change in how studios manage streaming deals for their content.