It means that poetry is a use of language that is exceptional in some way. If everyone can do it then it's no longer exceptional and the word loses its meaning.
Again, so easy to say. But there's no evidence that this is true.
Art and media have only increased in quantity over the years. When I consume some part of it, my enjoyment isn't any less. I still experience bliss and joy and get meaning from art in all the proportions I always have. And given how much people still deeply care about it all, so does everyone else.
The assertion that more of poetry means poetry becomes worthless hasn't got anything going for it.
Much has been said about how music has become a commodity. People today are much less likely to listen to the same album over and over, instead quickly moving on to some other song out of the endless offer on streaming services. Quantity has definitely changed consumption.
Moreover, in literature there has been a perception that the sheer amount of things on offer today has led to reduced interest in longer works, they become seen as more challenging than before. Dickens' doorstop novels were written as popular entertainment but today few have time for them.
Art and media have only increased in quantity over the years. When I consume some part of it, my enjoyment isn't any less. I still experience bliss and joy and get meaning from art in all the proportions I always have. And given how much people still deeply care about it all, so does everyone else.
The assertion that more of poetry means poetry becomes worthless hasn't got anything going for it.