I live in a nice, quiet part of the countryside where we don't seem to have thieves. Having said that I don't think the time has yet come in the UK where the type of people that steal things have realised the value of these cables, and as things stand at the moment there would be very few customers for a stolen cable. Where I live in Scotland I think I might have the only (semi) EV. I work in a main dealership and we've never had any sort of plug-in EV (although I saw one of the mechanics watching a training video on electric cars the other day - so you never know) and even if we did there would be nothing to plug it in to. However as EV's (perhaps, eventually) become more mainstream I've no doubt that cable theft will become more of a problem. They'll probably get stolen just for the copper content. The manufacturers will no doubt have to consider further the theft of cables - just as they've always had to consider the theft of fuel.
I'd agree about not parking on the cable though, I'd say that if this was done repeatedly on the same section of cable internal damage to the wires would occur. My Mitsubishi charging cable - after around one year of fairly regular use - has developed the well documented fractured cable fault where it enters the box part that has the lights on it. I've seen the YouTube video so I'm hoping to fix it. I now have a Rolec on the front of my garage (non-tethered cable) which is a much more robust solution to regular charging.
We recently discovered where I work that industrial power washer hoses don't take kindly to being run-over by cars either.