I'd say it's more down to the staffing costs than anything else to be honest.
It will be down to staff costing, due to the fact that the attraction isn't an Up-charged attraction, the acting costs are covered like the rest of the rides. Let's work this out roughly;
It costs around £500 - £600 per hour to run an attraction around the same size as Saw Alive, basing it on a figure of 6 actors and minimum wage, smoke fluid consumption, lighting, sound, electrical costs, management etc.
On quiet days, you can see why they don't open it, it's just a drainage of money if not a lot of people are visiting the park.
the fact Saw Alive is no longer open all year shows they are not that popular.
Sorry, but this isn't true, at all in fact. There are a LOT more year-round attractions destined for the UK. I know for a fact because I'm working on one or two at the moment that are in the stages of planning. I can think of at least 5 that are appearing in the next 2 years.
Market Research into the Scare/Haunted Attraction Industry will prove that a lot of people (GP) would actually like more year-round attractions to the UK. I've got documents on this very Mac that show this for a fact, I'll try and get quotes and upload them in a message to you if you'd like?