I have noticed zero F availability on the EWR-SFO/SFO-EWR sectors for a while now, and I have checked a few dozen dates, including both weekdays and weekends.

While I have noticed a growing deficit on EWR-West coast trans-cons, I am usually able to find a least one flight a day (sometimes not) with availability to/from SAN, LAX, SNA, SJC, PDX and SEA.

West coast to IAH does not seem to be much of a problem (including SFO), but I have been having an increasingly difficult time finding IAH-EWR F seats, especially (obviously) on Sundays.

My sample, of course, is not scientific, but it does represent a growing trend.