Because they look like crap. I do understand that trainers/"sneakers" are acceptable footwear outside of the gym in North America. This is not true on most of the planet. I'd easily get turned away from most restaurants will clip less shoes (I always carry a bow tie with me if I don't have a jacket.)

And a fair bit of pubs won't allow them depending on the flooring they have (mostly solid wood).

It's not a workable option for people who use bikes as sole transport.