Not sure what you mean by this. There are currently over 87 million media files on Wikimedia Commons, and obviously there aren't 87 million different licenses. Like Flickr (and presumably some other image sharing sites), when users upload files to Commons there are default recommended licenses. A current default is Attribution-ShareAlike 4.0 (CC BY-SA 4.0): https://creativecommons.org/licenses/by-sa/4.0/deed.en

More information on reusing Wikimedia images here:

https://commons.wikimedia.org/wiki/Commons:Reusing_content_outside_Wikimedia

That said, it is indeed important to read and comply with image licensing terms. This is not just to avoid lawsuits from "copyright trolls", but to be fair to honest photographers (like myself) who just want to be credited consistently and appropriately for our work.