Why is 90% marketers failing in Internet Marketing?
Its because most at the time their marketing strategy ain't correct. Suppose, if you are trying to get sales for an eCommerce site then SEO won't help you much but which will do help you instantly is PPC Campaigns.
Most of them fail because they are basically newbies who says that they are experts. And fail to target the right audience and keywords.
The 90% failing in Internet Marketing are the people using the inappropriate strategy for their campaign.
There are plenty of reasons such as wrong marketing strategy, wrong keyword selection, product failure to meet customers expectations etc.
People fail because they are dumb. Most marketers present themselves as experts which they clearly aren't.