I don't understand, especially for someone with likely more knowledge of the industry than average, your dismay here. Flights to resort destinations are commonly designed around full holiday sales. As the departure nears and booking trends are recalculated, then further seat-only seats can commonly be made available , if there are now different forecasts. Maybe, maybe not. Saying the company 'lied' is quite inappropriate trolling, that's exactly how it was at the time.
It also aligns with typical booking patterns, where those booking holidays peak several months beforehand, while seat-only bookings do so just days/weeks before departure.
Do you get hacked at the supermarket if they charge you £2 for a loaf of bread, when 15 minutes before closing they offer the same product, but only if they have any left, at 20p ?