Brian Foster's signature tire needs to work well on everything, that lead to giving the FT1 a relatively smooth center section to make the tire as fast as possible. Turning is when an increase in grip is needed, so when you lean the bike over in a turn that's when the micro-knobs come into play.
The micro-knobs provide a perfect balance of surface area, stability and space in between for when the dirt might be a little soft still. Sticking up above the main surface a small amount allows them to sink into that slightly soft dirt and give an increase in surface area contact.
Those micro-knobs don't negatively affect stability or grip on hard surfaces though, the edges of the tread pattern are smooth tread blocks that help protect the sidewall on ramps or street.