I can understand abandoned houses but why would people abandon their vehicles which they could have sold elsewhere to make some extra cash?

Maybe they had to take a flight back.

They are leaving for greener opportunities. Wouldn't it make more sense to take all your assets with you to sell it, if required?

Maybe. This town seemed to be very remote. It may be that road transport back to an area where the cars could be sold was not feasible.

Edit: Playing around on Google Maps, I was unable to find a driving route from the city in the article to any other major cities in the region. I think there may not be any car bridges and transport to the city may only be practicable by rail.