These trails were never designed or intended for motorbike use, but that is essentially what is now happening.
A similar thing happened with off-road 4x4s. During the 50-80s off roading was a niche enthusiasts pastime that took place on legal, often ancient unsurfaced highways or at infrequent events on private land hosted by interested landowners and organised by specialised clubs. The activity was done mostly by people who worked in the countryside or who had connections to the land (hence access to 4x4 vehicles) and because of this connection they understood the responsibilities and behaved sensibly. 4x4 use went largely unnoticed and everyone was happy.
Then at the end of the 80s something profound happened. Car manufacturers started making and selling 4x4s as lifestyle commodities rather than the working utility vehicles they had been up to this point. They sold like hot cakes!
Initially nothing changed, because nobody wanted to trash their expensive car and ruin the financial residuals by battering the cars over rough, rocky ground or squeezing down scratchy, overgrown old roads. A decade later a glut of older 4x4s hit the market and after suffering painful depreciation due to the sheer numbers now for sale, cost of maintenance and obsolescence due to newer models these were now affordable as toys for the ordinary man in the street.
This is where it all started to go wrong. Suddenly hoards of 4x4s were heading into the countryside and convoys of vehicles were chewing up the fragile lanes due to unprecedented volumes of traffic on roads that were only ever expected to carry a handful of ancient 'vehicles' a day. People had their 'rights' though and they used the lanes regardless of the weather or road conditions, and to make matters worse they often deviated from the track to 'play' on interesting features on surrounding private land. In conjunction with this and maybe more closely related to the MTB trail centre situation, was the explosion in the 'pay & play' 4x4 events. Unlike early club events where an enthusiast club might hire a bit of interesting land from a private land owner once or twice a year to host a competition, enterprising individuals began running off-road events for profit and would hire sites almost monthly or even more frequently in some cases, and squeeze hundreds of 4x4s onto the site to do as they pleased. This obviously wrecked the land, in a way that will take decades to recover in some cases, but also drew anger from locals due to speeding 4x4s tearing through the surrounding villages dropping mud everywhere. So now we have mass inappropriate use of countryside rights-of-way with illegal use of surrounding land. We also have private sites that have closed down both due to the permanent land damage and also due to the problems they caused in the surrounding community. It's no surprise that the rise of the anti-4x4 movements have been so successful, leading to closure of R-o-Ws and private sites.
Does any of the above sound remotely familiar? Irresponsible use of readily available machinery in the countryside.......
'Pay & Play' events are now much less common because the sites have been shut down by the councils or the land owners realised that the use was too extreme, unsustainable and damaging. Lets just hope the same doesn't happen to mtb trail centres (or maybe it should?)