On the other hand...
The route is NOT legal for motorcyclists, and mountainbikers and horse riders should expect to take reasonable care, always being able to stop in the distance they can see etc as the route will be being used by families with children and dogs etc.
The other motorcyclists were able to see the gate and stop in time.
To quote the great Kevin Schwantz when another rider moaned about a bale that had been knocked onto the track:
"Yes, but it was also possible to miss the bale"