Your argument sounds like its coming from the view of a season ticket holder, and in that regards I can understand it, ... its pretty natural that season ticket holders do sometimes get a bit miffed when they've paid their money upfront and then the club announces 'cheap offers on single matches'.
But, as been pointed out we are where we are (League 1). Lets face it the non season ticket holders aren't going to rush to watch Colchester. (no offence intended).
As somebody who is actively trying to do the '92' with his lads, we went to a Championship game last season because it was the school hoildays and I for once had a free night. My lads were 9 and 8, I enquired for tickets in the away end (for obvious reasons) and was quoted £66. The home team were running an offer, 1 adult, 2 children £25.
There was a huge number of families in the section we were in, many of the kids obviously going for the first time, perhaps with parents who don't normally bother. It put 4,000 on the average gate and gave them their highest gate of the season. The number of kids who were asking to go again at the end was astonishing.
Many won't of course, but some will.
Ultimately, United take the view as many clubs will have to, that at times, its better to get 50% of something, ........rather than 100% of nothing.