Could be-off season.

OR there are again some essentail works along a short portion of the line-and SNCF cannot be bothered to organise a detour-many normal railline are closed nighttime, as there is then no staff in the supervision centre.

OR-quite other way-this is also in the midst of the peaks of the FRench autumn holidays and it may even be booked solid, like by the boyscouts an an organised outing-or at least that part (it gets joined with other portions from else on the way). BTW-it does NOT use the main stop in Mars, but Blancarde, a suburban stop, to avoid going in-change direction-and out

OR-there is a strike again-they like to do that in FRance-but thats likely still a bit early for now to know

May sound strange to you-but use the planner of bahn.com -so often mentioned here-works far beter as app and covers eve more of EUR-and check-click on train nr and it will show more details, like also running days. The planner of connect sncf is often alas a bit murky. PLUS that 2 month before is the normal accepted period for advance-it may also simply be they are not yet all put ´in the system´.

Follow up: just checked-22/10 is SAT-and nites like sat/Sun are often out in off-season for overniters. You must have confused something.