How easy something is to steal doesn't mitigate against the theft. The delivery guy is going to be punished by his insurance company.
No idea how the female was involved and the story doesn't make it any more clear.
The guy who actually stole the car is on the hook for everything that he did.
My narrative would be the delivery guy left the car unsecured, possibly running and the male suspect and his skank walked by and noticed. Crime of opportunity.
Male says to skank let's grab it and go for a joyride. Skank is a passenger but knows the car is being stolen. Besides stealing the car, the male makes a bunch of stupid driving decisions.
The delivery guy appears to have failed to secure the car. Stupid but it that a crime? He will lose income until he gets a car back.
RM, I'm going to make some assumptions about you.
You probably have a respectable job that could be affected by criminal activity.
You probably have some amount of property and enough income to disqualify you from legal aid.
You probably have intellectual friends that wouldn't enjoy hearing about you getting involved in petty theft and drug deals.
You probably haven't spent time behind bars as a prisoner
The skanks are probably much the opposite. Basically, nothing to lose.
Humans are very adaptive to situations. Construction workers get used to hot, cold and wet weather. Letter carriers get used to slippery walks, heavy loads and barking dogs. Medics get used to seeing blood and bent limbs.
Career criminals and associated losers get used to prison. Three hots and a cot for life (USA) in some cases. Pecking orders are formed and accepted.
The ideal goal of Corrections is to convert the skanks to respectable people but what is the point if the days of misery for the victims outnumber the days of benefit from the reformed skank?