I was just wondering what would make a flight showing as wide open in Economy and Business fill up so quickly that they had a full flight 24hrs later.

Carrier Flight From Depart To Arrive A/C St Availability
9W 121 LHR 20:45 DEL 09:45 +1 77W 0 F0 A0 C7 J7 Z6 I3 P2 Y7 M7 T7 U5 N5 L3 Q2 S2 K2 H0 V0 O0 W0

Above is the availability checked around 20hrs before the flight. Next day the flight was jam packed.

I have checked to see if any other flights got cancelled that day and nothing. Are Jet just showing a lot of cheaper classes to fill up the plane in the last few days?