It's not 'fendering' the fenders, it's covering them - it's part of the fender. If it both makes them last longer and slide up lock gates better, what's not to like?
A traditional rope front fender will start to fray and wear out quite quickly; a covered one will last years, even decades. Why wear things out and replace them for the sake of it? A fender is there to do a job, yes, but it's not meant to be sacrificial.
Some people do just use a tyre (or two - wasn't there a photo on the forum recently?) but they don't give the same protection, and it's a devil of a job to get them to stay in the right place.. If something has been tried and tested and used for decades, then there's probably something going for it.
But surely that's exactly what a traditional rope fender covered with a section of tyre is. (Apologies if that was deliberate irony)
That's not Naughty Cal in the photo then...