I don't think trials not being a spectator sport has anything to do with the amount of participation. Harescrambles in my area get a large turnout...and HS is waaaay worse than trials to spectate.
I went my first National at Nebraska this year. My dad went also just to see it. He's in his 60s and did a little walking and got to see a good 6 sections. U could see 3 different sections just off the parking lot.
To me, that's far better than any Harescrambles spectating.