In one of the interviews in the MotU mini-comics collection, they mention that they had print runs larger than the most successful full-size comics ever, "I think 6 million".
In the peak years of 1985-6, each figure either came with a unique mini-comic or shared theirs with a second (like pic related, Modulok and Thunder Punch He-Man). If we assume unique comic = 3 million printed, instead of the character being produced in double quantity, that's still 3 million of each action figure for English-speaking markets alone.
That's almost enough for each of the 3.6 million boys and girls who turned 5 in the USA to own each figure.