https://jungleofferwall.com/
Like with CPP (cost per click) and CPM(cost per 1000 impression) there are different tiers from different countries because certain countries bring in more profits than others so the high-profit countries get the most surveys and the most traffic. The higher quality the traffic the more you are paid. First world countries will get the most surveys and offer to complete.
USA, Canada, Netherlands, Belgium etc. wealthier countries are considered tier 1 (highest pay)
Then there's countries from South America, South Africa etc. considered tier 2 (medium wealth, medium pay)
and lastly there's India, Russia, Ukraine etc. these are tier 3 countries (lowest pay)
Tier 3 is not mainly poor but advertisers spend less money on these countries both for CPM and CPC so there's a lower payout aswell because the site's owner simply cant pay more then what they get paid.