I think it's because, yes, many of them believe that they will be the "next muh big thing."
But, also, you have to remember most schools don't teach people the values of free and open source software. Most schools teach people how to be perfect little cubical drones for whatever tech conglomerate they land in after they finish school. I think additudes would differ greatly otherwise. For example, I am a programmer and my friend Y is also a programmer.
I have never gone to school (yet) I have conditioned myself to be familiar with linux Operating systems and FOSS certified software. Y on the other hand called Linux "annoying" and uses proprietary bullshit like microsoft and is confused by GCC compilers. He says programs should just compile for you.
Techies today are streamlined for performance under massive tech conglomerates like google and Microsoft not for working in tandem with other developers. In fact, as par the Marxist tradition and understanding, capitalism actually creates antagonisms between developers as people working for specific brands can't actually work with other competitors of the brand they work under. The economy as it sits today is rigged against us in every way you can imagine.
We are conditioned to see ourselves as individuals free from external stimulus not groups of people working for a common goal from the start.