Your views of a “spectator sport” might be skewed by Nascar or other good for tv Americanized sports with plenty of scoring and announcer drama. On-TV cycling is a “hang” and on the side of the road even more.
Well, no. I went seeing some stages of the Giro d'Italia. Time trials are awful on TV but great on the street because you see every single athlete passing by you. Normal stages are great on TV (3+ hours of live feed) but awful on the street because you don't see anything and you know little of what's going on. However in both cases it's great to be at the start, maybe a couple of hours in advance, or at the arrival, especially after the end.
Ciclocross is different. They have as much as 100k paying people (on venue) in the Netherlands and in Belgium. It's also great to be able to move around the track and see the cyclists in different spots. Probably this is possible only in smaller events. I have experience of races in Italy.
MTB, no direct experience. Looks great on TV and YouTube.
And if all cycling would go on pay TV, goodbye. I'll be a little sad but I'll look at something else. I'll keep cycling tough.