Downloaded InstallMacOSX.pkg gives an error of "This version of OSX 10.11 cannot be installed on this computer." Why? I downloaded InstallMacOSX.pkg to create a bootable USB drive and install OSX El Capitan on a separate computer.  That computer was shipped with El Capitan.

So, I am not installing it on the computer that is creating the bootable USB drive.  Why does it assume that the OS is being installed on the computer that is creating the bootable drive ?

So in order to create the bootable USB drive, I have to run it on a computer that is also running El Capitan, which is weird.

Is there any way around this?  I'm thinking of maybe using Pacifist?
Can't you just do a reinstall of macOS on the other Mac by reinstalling OS X El Capitan that came with a Mac. This link will explain: https://support.apple.com/en-us/HT204904.

Also, make sure that the disk is formatted HFS or HFS+ not APFS.

Good luck!