Off only the top of my head.
-Potentially faster installation
-Free
-More control
-Many distributions from LinuxFromScratch to Mint, making it meet the interests of nearly every demographic
-Wonderful sense of community
-No spying
-No bloatware depending on distro
-No ads
-Many window managers supporting different workflows
-Incredible command line power
-Easy installation of software with package managers
-Less malware
-Fully customizeable ux/ui
-Can uninstall anything you don't want
-Will help you learn how a computer works at a deeper level if you want to