One major factor is that you've got to find them. And that isn't easy. While dogs are the best way to find them, they have to be trained and being a nation of cat lovers obviously doesn't help! Well, apparently you can dig for them without a dog but you need to spot the tell-tale truffle fly.
So I look forward to the day we sell the French some of our truffles if anyone can be bothered to look for them. Although selling at £2,000 per kg is quite a good incentive to get off your arse.