A few years back I had two TATLs canceled out for no particular reason (that I was told) and both were very light loads. This made me suspicious and a bit paranoid since, even though (a) folks here assured me that light loads would not have been the reason; (b) I have flown on many light-load TATLs since; and (c) as post above, there are some days that are almost certainly going to be light-loads but the planes are scheduled and fly anyhow.

Possibly relevant to what OP is seeing is something that I have noticed a lot in the last year or so, as my paranoia about light loads (coupled with a conflicting desire to get a light load light enough to ensure a 4-seat stretch in Y [rare, but hope springs eternal]), is that flights will still show 100+ empty seats on the seat map until very close to the flight, and still go out near full. I think that this can be seating folks from canceled flights elsewhere (including other airlines) but, more often, tour groups (students especially) who do not seem to have seats ticketed until the last moment.