I believe the reason that second hand clothing stores (at least - especially children's items) do so well in the US, is because there is very high demand for "designer" and "in most current style" items and the "need for new" is so high that unless the quality is very low we often replace before the life of the item is over. (children often outgrow clothes faster than parents can keep up) + some kids have so much their clothes couldn't possibly show much wear.
In a place where there is as low a demand for high fashion as Belize, and the average annual income is around $5000, larger families and close knit communities probably pass down what can still be used, the way many in the US give their used clothes to the Goodwill or Salvation Army.
I am sure most Belizian's subscribe to a very old New England saying - Re-use it, Re-cycle it and Use it up.
But yes, 2nd hand stores are great! my daughter works at one.