Where did the money come from for the people who will never have it run out?
Because driving around the world only costs something around $1500 - $2000 USD /mo, any kind of "good" retirement from a first world country is a LOT more than you can ever realistically spend. You bank account will always go up.
If you're in a smaller vehicle like your Jeep I can see it being under $2000/m. The retired people in giant Unimog overland trucks can spend hundreds per month on fuel alone. Maintenance on those trucks is expensive too.
I get around 16-18 mpg in the Jeep (it's heavy). Most Overland trucks I talk to get around 12-14mpg. They are also diesel, which is cheaper in virtually every country in the world. Maintenance can be a thing for sure, but also remember something like a big Merc truck or unimog is designed to go 200k kms easily without any real work done, where-as my Jeep is not nearly that durable.
Remember too, that $/month is almost entirely dependent on how far you drive each month, given that fuel is by far the biggest expense. If you have all the time in the world, you can drive hardly at all and just spend $1000/mo :)
[edit] However the prices have increased since I last looked. A truck dealership near me used to sell them, but not for $100k+
If you stay parked somewhere for a long period of time sure, your costs will be low. But in that case it doesn't matter what you're living in, maintenance costs will be roughly the same.