The article didn’t seem to make the case for independent chains dying off. They only said corporate chains grew.
My personal observation is that there are loads of independent pizza joints. Many are probably not categorized as pizza restaurants as they serve many other dishes so they are probably not included in the numbers given.
I have more than a dozen places that serve pizza as a primary menu item in my little town. I live near a really small town of 250 people and it has two places that serve really good pies.
The article stated that over 2,500 independent pizzerias closed last year. Examples may differ in your area, but this article maintains that local pizza joints are facing stiff competition from the big boys and smaller, higher end crafted pizza type outlets. I believe this is true for every kind of retail operation, be it a decor store, a hobby store, clothier, etc.