The quick answer is that there is a set of formula that can be used for point multiplication so that a computer can quickly compute privateKey*G. However, there is no known set of formula yet for point division to quickly compute publicKey/G. It is not even known in mathematics if it will be possible to find such a set of formula for point division.

I don't have time right now to go into much more detail than that. Hopefully someone else will stop by to demonstrate why it is difficult with currently known maths.

This one is quick and easy:

https://www.youtube.com/watch?v=ZloHVKk7DHk&t=3sedit: The difficulty to compute publicKey/G is a little bit like root calculation. It is easy to find out the numer in one direction, but a lot more difficult to calculate it in the other direction. calculating 3.8

^{2} is pretty easy (3.8*3.8=14.44), but to find out the root of 14.44 you'll need a lot more computation.