A friend of mine recently returned from Cornwall where he rode part of the Camel Trail and remarked that he was "stunned at how ridiculously busy that five miles of former railway line from Padstow to Wadebridge, was with family cyclists, given that its not particularly interesting landscape."
Actually, I think it's no surprise that it's popular. Back in my days as a cycle promoter in the UK I travelled a lot between different towns and the most common excuses that people would give for not cycling were that they didn't like the traffic or that they didn't like the hills. In reality, not many people's journeys will involve that many hills, but telling them not to worry about traffic basically doesn't work. People won't do things that don't feel safe.
The Camel Trail is one of very few places in Cornwall which has both good subjective safety due to segregation and has the hills levelled out. For many people, this makes it well worth a trip (generally by car) to ride on the trail - even if the scenery isn't actually all that interesting.
Put segregated infrastructure within reach of everyone, and everyone can make other, more useful, journeys by bike. There is a huge pent up demand for cycling. Everyone already knows that it is good for themselves, good for the environment, saves money etc. The reason that many people are not cycling already is that the conditions are not pleasant enough for them.
If you've enjoyed riding the Camel Trail, or a similar route, come over here to the Netherlands for a longer cycling holiday always with very high subjective safety on longer, smoother, wider paths. The photo shows a cycle path through a field here in Drenthe which is sometimes a bit too popular - and not necessarily just with other cyclists.
(Yes, I know I've misquoted "Field of Dreams", but this way it makes more sense for the blog. I also know that the Camel Trail is actually a bit more than 5 miles long.)