People in Central America don't really travel light. Actually if you crunch the numbers, unless they are visiting family or friends, most people don't travel... well, not for the purpose of sight-seeing or holidaying. Usually if they are on a bus or... on a bus - there aren't too many other economical options - they are there because of something related to earning money. For example, they may have big bags of merchandise with them, filled with something, anything, which they have discovered fetches a better price in a location far from their home. Or they may be bringing back something to sell at home, which they purchase for a lot cheaper from far away places.
Anyway, whatever the reason, you don't often see too many humble, Central American folk travelling light. They usually have enormous bags and squeeze all their children onto one seat, or onto their laps, to avoid paying for an extra ticket. In Bolivia there was a woman on my bus that had so much stuff - in addition to her children - that she had to stack it in front of her legs and on her seat. As a result her head was almost touching the luggage compartment above her as she sat during the journey.
It's just the way things are done over there.
The above photo was taken at the customs check-point at the Panama-Costa Rica border. The people above are actually travelling relatively light.