These may seem obvious, but I have seen them all!
1. Your concept is not unique. Too many would-be entrepeneurs see a successful online business and think “If they can do it why can’t I?” Well, there are probably a lot of reasons, not the least of which is their headstart in the market. Are you prepared to outspend an established business in marketing?
2. Your concept has limited appeal. Such a small number of people would be interested in your product or service, that cost of marketing to those people would put your project in the red.
3. Your target audience doesn’t have money. Marketing to a segment of the population that is frugal or has limited spending power means little or no money for you.
4. Your product or service is available elsewhere for free. Even if it’s a little better, free will always win.
5. Your concept is so unique that people won’t know to search for it. In this case you’ll need to build demand and educate the world about your product or service. Certainly possible if you have a significant budget set aside to do so.