Is a Classic a Good Book?

Classics remained in print only if readers were buying them. If a title wasn't selling, it would not get reprinted. Digital printing means it is economical to print short runs. So there is seldom a practical reason for a classic to go out of print. But does a book need to have readers in order to qualify as a classic? In which case should publishers prune titles that don't sell? Being a classic is not necessarily desirable.