Slow growth is sustainable growth. When your influx happens over time such that it doesn't overwhelm the existing culture, the influx will assimilate to the existing culture. When the influx is large and vocal, there's more of a chance for the immigrants to destroy that very thing that attracted them. Reddit effectively became Digg when Digg imploded; once /b/ got a taste for F7U12 cartoons, F7U12 effectively became /b/. There's also the mechanical aspects of managing growth with a small volunteer team on hobby equipment. Hubski has the theoretical architecture to handle large influxes of people but practically speaking, a big influx of users can test its limits to the breaking point. Hubski's is an imperfect system that is steadily tweaked to accommodate the desires and needs of its owners and its users. Whenever your operating platform is reliant on "tweaks" you want things slow and steady.