Besides the argument of the potential that an app like Yo could have, it's also a business decision.

Developers have a limited amount of time they can spare to write code so they have to be wise with their venture choices.

At the end of the day, when you read that Yo was funded for $1M, bubble or not, it's a smarter decision after calculating the risk / benefit ratio to emulate Yo's model.

If their would be more funding in the areas described in the blog post, I'm sure more developers would launch start-ups around them.