It is technically a bug, cPanel assumes you can have 2 postgree and 2 mysql, which adds up to 4 in total. On free hosting however there is no postgree available however, but cPanel doesn't recognize that it is not part of the package.
Free hosting only allows for 2 MySQL databases. You can however reuse them for more then one script, separating each script with a unique prefix, this is unfortunately only an option if you do installs manually, softaculous can't handle specifying an already existing database.