Why is there no prefix for 10^5,10^-5 and 10^4 and 10^-4?

[ppppparker]

or, why was one never adopted?

 

[tommyxu3]

Just a convention? 10^3 a time?

 

[fresh_42]

or, why was one never adopted?

Myria for $10^4$ and dimi for $10^{-4}$ have been in use in France until the middle of the 20th century.
Today we use potentials of $10$ until $1000$ and then potentials of $1000$ which makes sense to cover the different orders we face. For everyday life we still have the small ones plus some special terms like hectares or acres.