I'll recommend someone else do the job. I've done that before.Fair enough. But you asked why people wouldn't do everything on the server. Backend independence is one reason. People in other niches may not want to send customers to somebody else because they're tied to the wrong database.
"... They ne'er cared for us
yet: suffer us to famish, and their store-houses
crammed with grain; make edicts for usury, to
support usurers; repeal daily any wholesome act
established against the rich, and provide more
piercing statutes daily, to chain up and restrain
the poor. If the wars eat us not up, they will; and
there's all the love they bear us."
-- Shakespeare: Coriolanus, Act 1, scene 1
