Time is right!
Well, the options are endless today which makes me think the industry is healthy allowing companies to entice us with new rigs.
I'm not sure that 4x4 ever really went away... When I was 16 in the mid nineties, it was a NICHE class. But there was a presence, for sure. It seemed like a black art, for pros and folks with the hook up to obtain the unusual and exotic replacement parts.
It seems to have been made more obtainable to the average racer because of the ease of today's race days.
10- 15 years ago your evening racing was taken up by tire cleaning, peak charging, discharging, motor spraying, crystal changing(!)
... all while attempting to keep your rigs dialed and replacing broken/worn parts.
Now we clean tires and charge batteries while maintaining the cars. Allowing for more time and money to put toward second and third classes.
I think that 4 wheel has always been there... just unobtainable from a casual racer's time frame and budget. At least, this is how I view racing 4 wheel as an adult.