LibreELEC for the Pi4 was not available at the time of the launch, so it was not included in the full version of NOOBS or PINN.
A Pi4 compatible version is now available online for download.
It will probably be included in the next full version of PINN, and I assume the same will happen for NOOBS, but it's not for me to say.
Bear in mind, that there is a limit to the number of OSes that can be included in the full version of NOOBS/PINN without RISCOS becoming unable to be installed, and now with 3 different versions of each OS to include,this may limit what can be included.
It just takes time for these additional OSes to be made compatible and included, but they will always be available online first.
I will be adding more to PINN as they become available. AFAIK, there is only Raspbian, LibreELEC and a test version of Raspex based on Ubunutu 1804 that are available for the Pi4.
PINN - NOOBS with the extras... https://www.raspberrypi.org/forums/viewtopic.php?f=63&t=142574