Why are the fires always listed as "under investigation"?

Who are these people.  What happens to them once arrested, tried and convicted?  

Do they serve time?  Why do they do it?  How do we stop them?

Wildfires are discussed ad nauseum but the causes and what is happening to the perpetrators is not.

One example - the largest wildfire in California history burned last year.  It was started by a University professor.  Actually, it was several fires started by the same guy that merged into a single burn.

1. August Complex
Acres: 1,032,648
Cause: Under Investigation
Date: August 2020
Location: Mendocino, Humboldt, Trinity, Tehama, Glenn, Lake and Colusa counties
Structures: 935
Fatalities: 1

2. Dixie Fire
Acres:700,630 (as of Aug. 20)
Cause: Under Investigation
Date: July 2021
Location: Butte, Plumas, Lassen, & Tehama counties
Structures: 1,225
Fatalities: 0