SBC has a duty to get the best deal for its council tax payers, most of whom (obviously) are not Town fans. So they are duty bound to drive a hard bargain.
Like they do when they sell off council owned houses?
Not sure what the exact legal requirements are for a council disposing of assets but I doubt it's as clear cut as you make out. There is an easy argument that a successful football club is good for the town, a good proportion of the town back the club (40k to Wembley for example), the redevelopment would be good for the area, the club get involved in community events and so on. Which could be used to justify a low price.
There are other factors playing a bigger role. The council can't sell it cheap only for someone to then make a massive profit out of it. The previous financial mismanagement at the club. The council seeing it as an way to make some easy money. Probably some others as well.