Just an anecdote from here in CFL: road races are gradually declining *but* we just got a new TT series which is very well attended due to its location and the course.

Training on the road has plummeted but the number of people riding gravel has exploded.

Here's some recent data for road racing in Northern CA (NCNCA). It doesn't have # racers going back past 2014 and it doesn't show field sizes. It's clear that road racing here peaked maybe 6 years ago. Field sizes are quite a bit smaller this year than they were two or three years ago, especially in the entry categories, but there are still a lot of races. Gravel races are growing each year. Cyclocross racing was big for a few years, but has essentially completely died. Lots of people riding cross/gravel bikes these days though. These are in large part the same people who used to road race.