When you start a Rails or Django project you're using a template. When you use Bootstrap you're using a template. When you use the business model canvass you're using a template. And forget cheap, those templates are free.
People use templates in successful projects all the time. Don't generalize. I'm sure a lot of sites have found success in their niche using themeforest as well.
If you want to compare apples with apples then it would be better to compare Bootstrap or Rails with some of the "framework" themes (like Genesis) that exist for platforms like WordPress. They stop short of design and mostly provide the designer and developer with a common language.
A complete theme usually has a lot more than just tools, conventions and code examples. It's a complete design, and content implementation, all you have to do is stick in your logo and copy and you're done. Not exactly the same process as using a framework.
Although I also dislike frameworks (Bootstrap high on that list) for the same reasons (shoehorning is encouraged) I don't think it's an appropriate comparison.
People use templates in successful projects all the time. Don't generalize. I'm sure a lot of sites have found success in their niche using themeforest as well.