PPPoE refers to Point-to-Point Protocol over Ethernet. The "P-t-P" you are seeing is specifically "Point-to-Point".
What this effectively means is a method of tunnelling an internet connection over an ethernet network, most likely through your local exchange. This works by you being given a local IP address for your modem and then the address for the remote machine that you need to use as a gateway for your internet connection.
As per that Wikipedia article:
By using PPPoE, users can virtually "dial" from one machine to another over an Ethernet network, establish a point to point connection between them and then securely transport data packets over the connection.
The machine you are "dialling" (the remote IP) is going to be the gateway for your internet service provider.
The reason it always shows up in an outbound connection is because it has to in order for you to have a valid internet connection. I suspect that the reason it does not show up on an incoming
tracert may be because it is not actually your machine that is getting the connection. You may well have a disposable "local" IP address that is not seen outside of your local telephone exchange.