Better alternatives for next time.
To reinforce what has already been said, and as one who spends a lot of nights sleeping in my van, the last place I would stop is a rest area. As mentioned the 24 hour truck stops and other businesses are generally safe, with permission. Permission is most important as vehicles which look like they are just parked are often towed.
As Michael said, FL introduced security at rest areas after a whole family was murdered, years ago. In MS there are rest areas with overnight security. You see the signs on your approach. I still always speak to the security officer, and ask where the best place is to park. Then they know I am there, and keep an eye on the vehicle overnight.
Like eveything else, just because you got away with it this time, and I am ever so glad you did, don't assume that it is always safe. Try to make better choices next trip.
Lifey
It's all about safety and security.
No such thing as a stupid question. I'm glad you asked.
For me the biggest difference is the security. Brightly lit with people coming and going all night. You have told the management that you will be there, and they told you where to park, meaning they will keep an eye on you. Furthermore, many have extra security all night long, and the local constabulary regularly loop through the lot, even if only to get a coffee. All this helps to keep trouble at arm's length.
Lastly, should anything happen you have somewhere to go or hitting the horn would soon bring management/security to your vehicle.
As Michael said, truckers often do not have a choice. But then trucks are not as easy a target as cars, though I have read about loads been stolen from trucks at rest areas.
Lifey