In fact, "low" is just as available now as it was one year ago as well as six months ago.

It appears that the OP mistakenly was thinking that he/she was posting on the Delta forum, or maybe even works for Delta, in light of the fact that Delta ensures that "low" is available and bookable on only 6% of all booking attempts.

During the last 3 weeks I have booked "low" tickets on CO to HAN (on TG), TPA, PWM, BOS and FCO. My TPA flights for this weekend were booked 3 days ago, incidentally.