They get scratched out then replaced with new ones, so someone is making a real effort to get their message out. I even saw one in Jaywick, perhaps they are all over Essex.
They have to pay quite a lot for the right to do so. If they didn't, I expect ITV would cover all the matches, certainly someone broadcasting free-to-air would. I'd've thought the BBC would want to hang on to their funds to make programmes that otherwise wouldn't be made, rather than shelling out just so that some of the matches get shown without adverts at half time! Just about to watch England play Croatia, broadcast free on ITV!