Whether they are or not should be based on a combination of forecast and actual wind speeds, as only that has an effect, not whether it's raining a bit much.
But arent routes closing because of predicted weather. The same you have called upon above.
Do i think that sometimes the railway throws in the towel to easily. Yes, especially in yellow weather warnings, however we are about to get some exceptional winter weather by 21st century standards, and i will take the disruption if it prevents a stranding, especially with some of the level of snowfall forecast.
How is this similar? Wind speeds over a bridge is entirely different to build and maintain railway infrastructure to be resilient to weather, sure bridges also exist in railways and can become a problem / impassable due to wind speeds (and you cannot change that sometimes) but that is not the point, the point is about the snow and other normal winter weather.
RAIB quite literally said themselves the incident was entirely preventable if corners were not cut with its installation by the contractor. Network Rail could have ensured and done its job with the infrastructure in prediction that poor weather would return (as does every year) instead of sulking and shutting everything. With a bridge you're kind of limited to the elements regardless of what design you choose to build, with railway infrastructure (aside from similar scenarios of wind limits over stuff like bridges etc) like drainage systems and other essentials, you can easily build and maintain it in a way that makes a world of difference to handling the normal wintertime weather that should be expected in this country. It does however unfortunately come down to cost and effort. It's cheaper to guide the sinking ship to the bottom slowly than re-float it.
This storm forecast however isnt normal british winter weather, especially with the wind speeds predicted in certain areas.
With regards to infrastructure such as drainage being under designed, how much will you pay for every drainage and earthwork feature on the network to be upgraded to take in exceptional events and ensure you have suitable outflow for the water you are capturing/diverting.
So much of the railway decisions are based around detailed weather forecasting which is fine until you get an uncertainly pathed unusually strong winter storm hitting an uncertain location of cold air.