At the scale those agencies operate at that sort of coordination requires a level of bureaucracy, especially when you consider that we’re talking about intelligence agencies who are often, by the very nature of their jobs, looking at vague incomplete pictures of things.

We’re not talking about 3 or 4 agencies here, we’re talking more like 25 so without some sort of centralized department even knowing who you may need to email about any one thing is easier said than done. (And that’s keeping in mind that with just a small bit of a picture that the thing you want to talk to someone about could be nothing.)

That’s not to say that there’s no bloat in the US intelligence apparatus, but your comment feels like a wild oversimplification of the problem the agency was intended to address

In the wake of 9/11 it reported that the FBI/CIA/NSA all some information about the attacks before they happened, but no single one of them had enough of it to figure out what exactly was going to happen and when, and had no dedicated channels for coordinating on that sort of thing.

DHS was then (theoretically) created to solve that problem.