If you look at the copy of the settings file from /etc/logrotate.d/", you will find there is this option extension .log
.
This option means you are trying to append the .log extension to rotated files. If you remove this option and run logrotate again, you will find that by default the extension will be *.log.1 , *.log.2, and so on for the rotated files.
In a nutshell, remove the option extension .log
. Because the rotated files will take .log as extension.