Bittorrent clients and the need to open ports manually

Hello.
This post will not be in the form of an article, but rather in the form of an email to discuss the topic.
Everyone knows that Skype works perfectly "in both directions" even if the computer is not connected to the Internet directly. It is also known as implemented .
Question: why are bittorrent clients still missing that would work on the same principle? After all, everything is quite simple. Or am I wrong?
I will be glad to hear opinions.