Fairness only applies to "games" that you are playing - enter different contests instead. L
Blame your country's laws, not Instructables.
It does take time and money to research the laws and try to work within those laws. I'd rather blame the lack of interest in the web site from people who live in your country. If the site isn't getting a lot of hits from your country then its not worth it to them to invest the money to open contests up to that country. Though i'm sure the sponsors of the contests have a say in that as well. No since in having the prize go to a county that that brand isn't open too. These contests are about advertising for the sponsor and creating new content for the site, as well as getting the site more hits and ad views.
Sometimes it's the lawyers, not the lack of traffic - some countries with relatively large numbers of visitors to the site are having to wait longer than is really fair because the laws in their country are ridiculously complex or require strange conditions.(For instance, to be allowed to run a contest in Quebec, Instructables would have to move to Quebec!)
If you searched this site regarding that issue you would know why it is that way, the potential work around and what is being done to remedy the situation.