I still don't understand this.
Couldn't they make it explicit that the season ticket had this condition by, say, putting in very big, bold letters on the marketing material "BUY AT YOUR OWN RISK, WE MAY NOT BE ABLE TO COMPLETE ANY OR ALL OF OUR FIXTURES".
Seems we have foregone c. £2m in revenue by not selling STs, so I guess there must be an absolutely compelling reason.