"I'll skip over the political ax you tried to grind in most of your post (ER disposed of it handily), and address your concern that people wouldn't want to take a one-way trip to another star system. That doesn't match human history (and prehistory). Up until the era of the great sailing ships, nobody ever returned home from a voyage to set up a colony in a new land. They said goodbye permanently to friends and family, and if they'd returned, they'd have been treated as ghosts or demons."

That's not true. Mail has been something humans have been doing for quite a long time. And bringing the rest of your extended family to the New World has been a tradition that continues to this day. And trade has almost at all the times has been a part of it- and trade is pretty close to impossible beyond say a 20 lightyear distance- even with warpdrive. Now, if you can reverse time, that would change things- intersellar/intergalactic communication could be instantaneous.
Of course some people do commit suicide [about 20,000 per year in the US]. So my point isn't that no one nor group of people won't travel to different stars. My point was that as a civilization or government it wouldn't make much sense- and we won't be going to go to other stars because it's too crowded or we need resources- or at least we shouldn't assume that this could be a driving force.
Now things like a Sun going nova or supernova could change this.

But with warpdrive and the ability to control time one has other aspects to it. Why limit yourself to this Galaxy? If you can go at or very near lightspeed, difference between going 100 lightyears or 500,000 lys or 100 million lys isn't as significant as slowing down again [assuming reaching these types of velocities has any difficulty to it].

"Maybe it's more accurate to say that humans have always sorted themselves into adventurers and stay-at-homes. The homebodies have always outnumbered the adventurers, so perhaps you're right on a statistical basis. But that hardly means that when it becomes possible to voyage to another star, nobody will want to go. We' have to have changed out of all recognition, and lost all spirit. In that case we'd be on the slide to oblivion anyway, and we'd no longer matter in the grand scheme of things."

Ok, but the question is "Where the hell are they?".
Well, some could still in transit [they lack warpdrive] and some could still be in transit [precisely because they have warpdrive]. And (99.9999999999999%] who could come, aren't coming nor going anywhere.