I brought my first RC car in 1988 (RC-10), and started competitive RC racing in 1992, 12th scale.
What I have seen over the years that the popularity of any particular form of racing goes in cycles. On road will drop while off road gets more popular, then it switches. The changes cannot be linked to any particular event, it just happens. Off road has gone from loamy dirt, to hard packed clay, to now carpet and astroturf. (Off road carpet is an oxymoron)
The one thing you can count on is there is a strong but small base for every form of RC racing, so it will always be there. It just may not be on the level that we want.