There's probably a decline in that hobby, I'm just not aware of it because I don't know anyone who does it.
With modeling, trains, and balsa RC planes all declining, I can see how hobby stores would struggle.
The last two physical hobby stores we had locally closed within the last 2 years. Now we have none.
Both redid their stores inside and set up all new RC car racing tracks, and both were nicely done, but it didn't save either store.
So not even RC cars seem to be as popular I guess, even when a race track (a place to race them) is available.