If that was the case they'd reduce the payload, not cancel the flight!
Fathom,
Full tanks are full tanks, reducing payload/blocking seats doesn’t miraculously produce more fuel when the tanks are already full.
What I was implying, (perhaps a little too subtly), was that maybe with the enroute winds and TAF for arrival, full tanks was less than the min op fuel required, even with no pax/freight.
RD got it.