They're fun little cars, with very wide appeal. They're popular restoration projects due to their simplicity - great for the novice restorer, like me, as they can be used as a learning curve for restorative techniques and also their toughness - if it's been abused in the past the damage probably won't be too severe whereas many classics would be irretrievable. Their toughness also means that once running they don't require all the TLC and messing about that goes with running a classic.
And then there's the costs - good Beetles are appreciating over here in the UK, and it's often a lot cheaper to restore a crocked one than to buy a decent one - not to mention much more satisfying .