WTF happened? Up into the 1990s they were hugely popular. Right now I couldn't even think of a local shop that sells them.
They were everywhere, my local shop got in a stash of 'Frog' kits selling for three shillings each, showing my age. I bought a Spitfire, of course, after badgering my Mother for the money. I even painted it because the shop sold a little paint set too, green, brown stripes until I realised there was an actual pattern. That spitfire even led to me meeting a real Spitfire pilot once.
The problem was that we kids that bought the models are still the people building models. Modern kids have various other distractions. But I wonder though is part of the reason kids aren't building kits is because the local shops don't sell a few Airfix or Revell? In the town I live the best place to buy kits was over a pet shop, strangely. But that closed. The local model shop caters mainly for R/C aircraft and Wargames workshop gamer geeks. The only places selling models are in the local toy superstore and an Art and Hobby shop with a tiny selection of Airfix and some Revell.
To be fair, I think Airfix is doing it's best to resurrect the the idea of selling in local shops as the odd one turns up in various places. I was passing through a small village called Borrisokane, County Tipperary and was surprised to see a selection of kits in the window of a shop. I went in and spoke to the owner. He told me he sold quite a few so it was worth his while. I left with with kit of a T80 made by Zvesda. It's a long way to Tipperary for a Russian tank.