What you don't realize is that this happens with ALL businesses and ALL entrepreneurs. For example, in a college entrepreneurship class our teacher had to make a rule about not writing a business plan for opening up a chain restaurant. In fact, most of the ideas from the class were opening a bar, restaurant, pawnshop/payday loan, rental property website, computer repair service business, etc. I'm surprised starting a used car lot wasn't a common idea, but I digress.
It's not just software developers who tend to follow trends. It is almost anyone who has ever tried to open a business. Most people aren't that creative beyond "I'm going to open a widget factory but mine will be red instead of blue" without ever considering any idea that is outside their everyday life experience.
This may be fairly well justified. When reading about successful entrepreneurs, I always try to figure out what the genesis of their idea is. Typically they seem to have industry domain knowledge before they start a company and not the other way around.
It might be that learning about a new industry is the best path to riches, but my guess would be that you're best off doing focused research on that industry for a while first (ideas: get a job in it, do consulting for it, go to industry conferences, read books, read industry forums and blogs).
I'd say it's a mix of arrogance and lack of education.
Arrogance because "woah, Facebook billions. I'm going social network direction" without any such idea to be better.
Lack of education can also mean lack of experience. Areas are: Business/Finance (Stocks, hiring, etc), creative skills, design skills and user experience skills. Math/Programming seems to be the fortitude of most of them but that alone won't execute well.
It's not just software developers who tend to follow trends. It is almost anyone who has ever tried to open a business. Most people aren't that creative beyond "I'm going to open a widget factory but mine will be red instead of blue" without ever considering any idea that is outside their everyday life experience.