Social networks can be dominated by one sub-population.

If it catches on with one sub-population too quickly, other sub-populations see only content from the one population and think "this isn't for people like me."

You want a roughly equal adoption across a diversity of sub-populations.

This is what happened to Friendster and Orkut.

It takes only one "super-spreader" adopter within one sub-community of a good new product to get stuck in a niche like this.