These are not vanity publishers, but proper, royalty-paying publishers, who buy only a small percentage of submissions, edit carefully and pay for all the preparatory work. Producing an e-book is not much different from paper publication. The book is edited, proofread and is publicized by various methods. Reading it is different, however. You do that on your computer, or you can print it out to read.
Nothing is wrong with paper books, but currently e-books complement paper books.
There are times when they are far more convenient. I m off to the UK in two days and will take along several e-books on my laptop. E-book Readers similar in size to books are now being manufactured. Or you can read them on palmtop computers. E-publishers are producing a wide range of books.