If that were the case it would be easy enough to legally acquire any number of prescription drugs to gently shed these mortal coils. No need to splatter your brain matter all over the landscape for your family to see.
That may be why he did it in his office.
And men are more likely to use guns for lots of reasons. It’s a more decisive executive action. And billionaires probably don’t give much thought to cleaning because it’s been done seamlessly and quietly for decades.
He’s also from the generation that prefers facts to feelings and all that squishy touchy feely crap. And they don’t want to go through every one else’s grief and processing to get their “permission”.
It may be selfish, but it’s completely rational.