There are a lot of Warhammer models and the parent company "Games Workshop" is doing extremely well and expanding despite it all being built in Britain. One neat thing about Warhammer is that there are a LOT of books and video games as well, so the IP is very strong. There is always new lore coming out from the various factions too, so the models have special connections with the fans. I have 3 game stores in my medium-sized city that cater to Warhammer and there is always a game going on. Warning: it is a very expensive hobby.
There is also a lot of popularity with 3D printing. I'd check out thingaverse or other popular 3d model sites to see how many downloads are coming from WW2 and muscle car models to maybe get a feel why hobby shops are struggling.
Modeling never died. It just evolved a bit. If you were ever into the WW2 kits, I'd check out Bolt-Action if you're interested in wargaming with models. It's not as big as 40k, but people do play.