To sum it up in one word: visas.
Turns out walking thousands of miles is the easy part.
for another source,
https://www.msn.com/en-us/news/other/exhibition-charts-karl-...
I’ve driven my personal vehicles through 65 countries on 5 continents. It’s not that hard.
It's a bit mysterious how did he get from Russia to Mexico in 2006? The official website linked says just "displaced".