This guy carried out an organized domestic terrorist attack with help from others, actually killed someone as well as badly injuring another, and got only 41 years. Why the disparity?

The Federal Building where he murdered the security guard is just an administrative building; at least the people in Texas were motivated by the somewhat reasonable belief that they were attacking guards at a concentration camp.

https://www.justice.gov/usao-ndca/pr/steven-carrillo-sentenc...