I'm going to play Devil's advocate here, because there are a couple of things I'm a bit dubious about.
Firstly, it seems that they are comparing the game of 30, 40 years ago, with the game of today. The old leather footballs, and the muddy pitches of three or four decades ago, are long gone. And...
Secondly, you'd think there would be an awful lot more 'old time' footballers being diagnosed with dementia, after a career spent heading a football. It can't be just the famous names that are affected. Why don't we hear of more? In fact, you'd think there should be hundreds, if not thousands, of ex-players suffering. Maybe there are, and we just don't get to hear about them.

It could be, perhaps, that only certain players are affected. In the same way that some people are prone to cancer, or heart disease.