The reason is related to multipath interference effects on equipment such as the radio altimeters (everything in low visibility approaches is related to radio altitude) and localiser and glide slope track antennae.
We train every year and are reassessed at our ability to handle failures from such items as well as a whole other list of failures whilst operating in low visibility conditions. We must pass this in order to retain our low visibility qualification. If we do not for any reason then we are prevented from landing and taking off in anything less than 550m.
Should and interference affect the mentioned items, or anything else for that matter then we will exectute a missed approach. That may however have been our only shot at landing at our intended destination due to fuel. If we can't see an immediately obvious reason why the aporoach failed then we would be in Cardiff, Birmingham or Manchester from the last few days forecasts and actuals. Yes we do carry more fuel to allow more holding and another approach in such conditions, but if holding delays are worse than anticipated then it could be a single approach we hold fuel for before diverting.
Of course none of us wants to see the aircraft do anything unexpected or exciting close to the ground.