It is a very different issue on manmade trails though, that’s kind of the point.
I don’t think it is – have a good nosey at all the natural stuff you ride these days and think back to how it was when you first rode it…most have become motorways and straight-lined as it is ‘easier’/’quicker’ – the volume of riders has also increased – and with that comes a much wider range of skill – so the less skilled riders tend to miss corners and skid more and generally aren’t as confident on the trails that are pushing their abilities (everyone needs to push them often to improve).
The fact we now have designated areas for mountain bikes to ride ‘mountain bike’ trails, doesn’t remove the issue that riders will change the flow of a trail – it appears to be human nature.
Very few bikers genuinely sympathise with a trail builder – if they really did, they would give up some of their time and get involved – many people do (I’m one of them and I know many others), but in most cases, people just want to ride their bikes…so if someone spends time and effort building something, most riders will be happy to ride it – if it is too technical for them or what they think isn’t fast enough, they will modify the line – this happens at trail centres and natural trails all over.
I’m sure if more people did give up some of their time to get involved (even just once a year – it all helps) then they’d get an idea of what goes into the building part – it isn’t just people getting handed gloves and told to move rocks; nor is it sitting in an office drinking coffee and talking about new stuff – there is a huge amount of different jobs and stages that are done to get a trail on the ground…and for most, they are oblivious to the time and effort that is spent by the few.