Higher kicks to Jodan begins with the 3rd son of Gichin Funakoshi known as Yoshitaka/Gigo Funakoshi into the modern karate.

Gigo started to develope and change the classical Okinawa form to a new fighting method influenced by kendo, wereas his father was responsible for incorperate the philosophical part "Do".

At the time there was no other known styles that trained high kicks to the head. On Okinawa as we know there was the selfdefence aspect. So they kept the low kicks.

I also recall reading about a fight between Gigo and another instructor of a closefighting style (goju?) .It is said Gigo lost it!? but we can't be sure. To gain an advantage he started to develope new leg techniques. This resulted in that his karate form won some matches and slowly the other styles also started to incorperate kicking techniques.