Once you build a brand and get to scale, you'll dominate your sector, have real pricing power, and watch the profits roll in. For the few companies that have done so, it's unclear how much pricing power they have. The laws of economic gravity apply to online businesses too. Drop shipping from your supplier sounds good until you realize that they aren't set up to do it and, when they do, they largely serve to alienate your customers. Acquiring customers is very expensive, and most of these customers never return.
Viral marketing is nice when it happens, but exceedingly rare.
There are plenty of other applications and companies out there vying for every customer's short and fleeting attention. Most customers are quite skeptical. Try getting and keeping a piece of today's customer's attention. If you get the eyeballs, they can be monetized. Sometimes eyeballs can be monetized, but more often than not they can't, or are only monetized at a ridiculously low value.