From the FAQ:
The parklet is replacing a car space, and the motorcycle parking is turning into bicycle parking, roughly.
We (DNA) actually petitioned to get those 6 metered motorcycle spaces installed, way back when. But then in the intervening decade, the Cycle Gear motorcycle shop moved in right across the street from us, and they installed eighteen free motorcycle spaces on Harrison at 11th. They're literally 50 feet away.
Once the parklet is installed, if it turns out that the difference between 18 and 24 motorcycle spots on the same block is actually significant, we'll start the process of turning another car space into metered motorcycle parking. We'll see! Many members of our staff ride motorcycles, so we'll know right away.