Why don't they make 5 different harmonicas per key going from low to high?

Instead of just 12 harps - where somebody arbitrarily decided that G in first position is low and F# in first position is high. Why isn't there 5 F# harmonicas going from low to high, and 5 G harmonicas going from low to high, etc. There should be like 60 harmonicas instead of 12, no?