They could, but I believe the idea behind it is not having to check once a day. You get an email when a new chapter is posted, get a notification on your phone, then can read the chapter. The implication is also that they would like to read stories close to when they come out, not in one big chunk every day.
Personally, I think it's a good feature to add. It's a matter of convenience, like asking a pizza place to deliver. You could go down to the store and pick up the pizza yourself, but for most people it's far more convenient to have it delivered.