From what I think I vaguely remember hearing about this guy on a podcast a while back, there were areas he had to wait for permission or for conflicts to end before he could walk through them and he didnt want to go home until completing the journey so he would stay with friends in Mexico, but then fly back and begin the journey where he left off.

Here's his route:

Edit: from reading the Wikipedia entry and refreshing my memory, the delays were due to visa issues like Russia only allowing 90 days in the country at a time so he'd have to leave and come back every 90-day stretch but also ran into issues with funding which delayed things further.