It took your content for me to realise that deep green was used as "no data". seems unorthodox

In a round about way, it probably is geographically related. So few people live there due to the land being pretty useless, but not so useless that the people there are spread out and when county lines were drawn they followed county sizes similar to Midwestern states. More western states drew larger counties but had similar population density averages so the number of people per county are high enough that there are enough suicides that someone may actually be tracking that on an annual basis

Arbitrarily cherry picking that squished pentagon county in northern Nebraska, there are only 769 people living in the entire county . If just one of them committed suicide that county would be off the charts lethal at 137. So when you take the US average suicide rate per year it could take up to ten years for someone in the county to commit suicide. So there probably isn't anyone keeping real statistics in that county

Realistically I think this is a bad map since counties with lower populations get disproportionately amplified suicide rates

The tornadoes get you before the depression does

Not very many people.

It's because noone lives there.