The problem with the UK isn't that it can't handle a bit of snow, it's that it still surprises everyone that it can't handle a bit of snow. In the South, we get one major snowfall per year maximum, and it's often fairly localised (I live 15 miles south of LHR and didn't get a single flake). Comparing the UK to the likes of Scandinavia and Canada is pointless - they have snow on the ground for 4-5 months of the year in parts, if they weren't better prepared then these countries would be simply inhospitable.
The cost of gearing up the UK's infrastructure for such a rare event is absolutely not worth it, so we need to accept a little bit of disruption on the 1-2 days it happens. It's early December, the quietest time of the year for travel in/out of the UK. As with most disruption at Heathrow (Snow, Wind, LVPs), it can usually be linked back to the lack of runway capacity and terminal space. As soon as aircraft require extra separation or additional time on stand, the lack of extra capacity results in flights needing to be cancelled.
More embarrassing than the UK's ability to handle snow is the keyboard warriors on Twitter complaining about it, as if their life has been ruined because they had to sit on the aircraft for a few extra hours waiting for de-icing. But that's just the world we live in now.