Luton hasn't been bad but still two days of low temperatures to come. Also much of the course is outside Luton and it can be more affected by icy conditions
Also some of you might not know but two years ago (or was it three) on a day when the ice was not as bad as now, a car came down through Streetley, lost control on ice and over-turned on the route. It was about 10 minutes before the start which was delayed before finally having to give in and cancel the event. So the organisers are very aware of the issues.
I take the point on cross country, I am hopefully running one myself tomorrow but these tend to be run by club runners whereas the mass runs have a lot of recreational runners who are less experienced in the conditions. Also frozen grass is still easier to run on than frozen pavements in my experience.
I think they are also taking in account the conditions elsewhere for people travelling. In theory easy to come up from Brighton through London but the trains aren't running on the southern half at the moment due to horrendous conditions down there. If you are local you want them to delay a decision to as late as possible but if you are travelling then you want to know earlier.
Although not a direct organiser I am with one of the local clubs and in a moment of madness had offered to set up the start/finish early on Sunday so there is a part of me which is probably pleased.... but only a small part - honest