Our school and town dropped all the .mi.us domains and they have their own domains now, why would they do that? I know it used to be k12 too.

They nearly all did that because the average person never figured out how the DNS hierarchy worked, and many of them never even got comfortable with the idea of having more than one dot in a domain (with the exception of a “www.” prefix). So it was easier for each district to just make up a random .com or .org.