Why would somebody be driving through the Mojave desert in the middle of the night?

NICE!

Sorry, everyone has really good reasonable answers, but as soon as I read the prompt, the first thing that popped into my mind was. "To bury a body"

Which might be a little bit out there, but I think it could be interesting, the twist to the story, the dead body doesn't even have to relate to the main story just ads tension to what's happening because the drive has to hide it from others.

 

Jordan's off-road motorcycle club is having their yearly outing in the desert northeast of Hw7 58 and Hwy 395, typically labeled as Kramer's junction on most maps. The event starts in the morning, and he wants to get there, unload his bike, setup his camp and get a good night's sleep before the fun and games begin in the morning.

 

Saw this article, might be a use.
https://www.travelandleisure.com/trip-ideas/nature-travel/california-mojave-trails-national-monument-dark-sky-sanctuary-route-66

 

I lived the Mojave desert, meaning from my early childhood, I camped there for the desert 1000s and 500s. I then rode dirtbikes there literally in the middle of nowhere (way back). I did epic 4-wheeling trips there for days at a time when I was old enough to drive.
Then I took my son there with a shooting club and he learned to shoot safely, surrounded by old-timers, military, hunters, law enforcement, enthusiasts, and competition shooters. We were usually 30 - 40 dads and kids (even some girls and moms). Magical.
I drove lost for hours, looking desperately for even tire tracks to follow to camp, praying for first light to come.

The point I make here about Mojave is that it is living drama everywhere; Darkness, desolation, terror, freezing rugged wilderness, majestic views, glorious and dangerous flora and fauna, and you.
If you belong there (easy), it's a fantasy playland. If not, a harrowing nightmare. People have died there less than 1000 feet from help.
It is also teeming with life and activity if you look beyond your feet; trails, washes, county roads, US forest roads, old prospecting encampments, people, water, and sustenance.

Still, for a writer, Mojave is a wealth of real adventures and stories crisscrossed over land and time.
So, let me know what you want your characters to do there when 'driving through' doesn't work out for them. There's just so much! (yes, you will need Google Maps or Google Earth)

 

At a glance I would say I-15 through Barstow and Baker California it is a long lonely stretch on the route to Vegas.

 

That is not a lonely stretch of road anymore. The loneliest stretch of road around there is the section of 191, between Monticello and Moab.