I fly (as a passenger) on the Asia/ME routes quite often and almost always the economy sections are full - mainly maids and labourers on their first or second flight. When the seat belt sign is turned off after departure you can hear the clicks as most of them unbuckle. Why not? The sign said "buckle up" and now it's off!!!
Culturally, most of them live in a society where prohibition rules so when the prohibition is removed... . Try looking for a seat belt in the rear seats of a taxi in Jakarta or KL.
Why not leave the sign illuminated and make a cabin announcement that it's now OK to move about the cabin, IF YOU NEED TO.
And don't get me started on the rush to stand up as soon a possible after landing.