The author of Paint.NET purposefully included ads on their website which looked like download buttons. That should tell one all they need to know about Paint.NET (and Windows freeware).
It says something about the economics of freeware, but Paint.net is very good, an essential program for many people, and completely safe to install and run.
The website is trash but the program itself is great.
Install from chocolatey.org or ninite.com
It also used to be free until the creator decided to make it proprietary.
Some people just hate good things.