My thinking is that the people who say the servers were empty, didn't have any global chat channels, weren't in a SG and hung out in solo mission caves. That's all I can think of that would make the game seem empty. I played on Champion and was tuned into at least 3 channels just for forming TF/SF/Trial groups, and a channel for my SG. It was almost constantly buzzing! I never got the feeling that the world was empty.
For me, at least on Liberty - which seemed to have maybe 5-10% fewer people than Champion - on the weekend evenings, there were plenty of people about - provided the playerbase knew ahead of time that there was a reason to log on.
When @Cinderfrost would host Wednesday night iTrials on Liberty - sometimes we had to get two leagues going. But - the rub of it is - that's 48 players at most. Granted, not everyone wanted to play incarnate content. (or could, for that matter.)
On Friday and Sunday nights, @Noyjitat or @Noyjitat? or any of his other alt accounts, lol, would host MotherShip raids. However, sometimes there simply weren't enough folks to run them with more than a team or two. And, yes, I know an MSR can happen with less than 8 - but let's face it - they need to be a pretty solid, balanced 8 to get the job done.
After those MSR's, I'd host iTrials, and more often than not MoiTrials - Liberty loved their badges! Usually, I wouldn't have any trouble recruiting because I'd do the recruiting for the most part at the same time every weekend.
Sadly - when I would try to get task forces going over the weekend, or during the week during prime time - even the weekly taskforces - this was often a painful and tedious process. I had a fairly long list of global names to call upon, but once SWTOR went live, more than half of those names stopped logging in.
I can think of a dozen right now - I think I saw them once or twice pop back in before the end.
/begin digress
Granted, if I may give myself the benefit of the doubt, I was considered by most to be...passionate about the game. I took things way too seriously, in retrospect. (it wouldn't be unfair to suggest I was wound pretty tightly..okay, toilet-trained at gunpoint, maybe!)
That may have been a factor. I didn't suffer fools kindly - but a lot of that was trying to protect the game time of those few who could only play for a given hour or so each week and chose to join my leagues.
/end digress
In the end, I found myself playing on Infinity and Champion more as the end drew near. I'd had toons on Virtue and Freedom, as well - but I didn't team up that much on those servers. Most of the invites I got were for farms - which was okay - but I could always get xp faster solo than teamed. (when I take into account the amount of time to recruit and head to mission door etc.)
So, from my limited perspective, yeah, CoH was fizzing out.