There's always been silly startup ideas, but that's mainly because a lot of people are silly. The "playing house" thing seems to be a different phenomenon: over the last few years I came across people who were very smart, very driven, but completely focused on other people's opinions. They like winning contests and climbing ladders. Now that startups are becoming a respectable career path, more and more of these people are trying to start startups.
In the corporate world, you can always focus on the next presentation, the next interview, the next hurdle, and gradually iterate upwards. To build a company you need to think in terms of fundamentals, to think long-term, and to think independently: members of this type can be very good at producing polished and sensible-sounding market analyses but distinctly bad at those three.