Just how many millions of people do those outdoors activities?
You can't survive selling solely to YouTubers, that's definitely true, but you don't need to. Just like tennis companies don't need to survive solely on selling to Grand Slam competitors. Plenty of people are willing to spend a few hundred bucks on their hobbies if it gives them nice pictures and videos for InstaSnapBookTok and to show off at parties.
And no, normal cameras and smartphones are not enough. They'll do for a casual hike, but they will not survive being attached to a mountain bike going downhill and being shaken to bits. I found out the hard way, it is how I killed my first smartphone. If you disagree: why not try it out yourself with a $1500 flagship phone and report back how it went?
Many, but that's irrelevant. There are hundreds of thousand of bicycles in my city, and very, very of them have cameras. That's kinda the point: what you're selling is the dream of being a YouTube influencer, pretty much. Otherwise, there's little value to having a big library of videos from every ride you've taken, especially since let's face it, most people ride the same routes / trails most of the time.
Now, the dream of being an influencer may be a strong selling point, but you can only do it once. People are not gonna keep upgrading.