New cameras why ppoe and nat factory turned on ?

[Jack B Nimble]

Still new at most things but, I am trying still to get VPN on my router working but that is a whole story to its own. Why would the NAT and PPOE be pre installed to be on with my cameras ? I only noticed when I typed in my external IP and my camera log in popped up ? then went into camera settings on network and all 7 of them had NAT on with active ports opened. So on my browser typed in my IP not LAN one and the port that was identified in camera for NAT I saw log into camera. Is this a issue ? I naturally turned them all off but, wonder would NAT help me in getting access with Tinycam Pro when outside of my LAN ? This perhaps a good idea to check and turn off for most not needing them as well I assume as less open the better.
I don't want to open ports but thought hey if these work ? Now I will wait some blasts lol