They made the 20" rims before freestyle really took off, maybe late 70s? (at least they were around in 1980)
So while popular with freestyle riders for a bit later on, think they were originally designed to be a tough spoked wheel for racing
What I didn't know until I tried to find the actual first run of production is that they did them in 26" as well as 24" - never knew they did them that big!