Continuing on my earlier theme, I bet they felt killing someone for a truck would be easier (and more thrilling) than whatever DM would need to do to liquidate $24k. Or possibly easier and more thrilling than writing a check, if it comes to that.
Having spent so much time focused on the farm, I agree it is weird to discover how much of this crime took place in the hangar. My current thoughts are that DM fancied himself a businessman, and now that Dad was dead, the hangar was both his man-cave/toy storage and his place of "business". He felt more in control there.
The farm was for partying; the hangar was for business, including the business of illegally obtaining vehicles. So they went there to take care of business.
Sorry to frame it so callously, but this is my impression when I try to get inside their heads, and no it is not a fun exercise.