What follows is MOO... and with quite a bit of Occam's Razor applied, so, here it is:
Why is the bike ride not considered a likely scenario? Which CCSO statements and/or known discovered evidence indicates the bike ride theory as bogus?
The bike recovered down a steep hill along SM's assumed-typical bike route is fully simpatico with a roadbed abduction.
SPECULATION:
SM was riding along the road, wearing typical biking clothing (including helmet) and a vehicle approached to her immediate position, from either behind her or toward her and... in an instant the vehicle stopped. One or more perps exited the vehicle, they grabbed SM off the bike and one perp placed and held SM inside the vehicle.
Of course SM was still wearing the helmet, it was strapped on. Even a struggle likely wouldn't have dislodged the helmet since they're designed to remain on a head during a crash.
The perps had no desire to take the bike (it wasn't their target) so the second perp performed a quick bike toss into the ravine: it was then out of immediate site. That perp returned to the vehicle and off they went. They've driven away from the scene.
SM did not cooperate nicely, perhaps. The helmet had become quite the nuisance in the struggle so perp #1 managed to remove the helmet and toss it from the vehicle.
Perp's intent: sexual assault. It may have been an unplanned crime of opportunity or maybe the perps knew SM bike ride schedule. Either is possible.
What some perceive or have described as 'odd' or 'weird' regarding BM's behavior... it's reasonably explainable in light of the fact that the "love of his life" has gone missing and he doesn't know what happened.
I haven't yet discounted this theory.