Price discrimination. It's because it's not really the same product -- one is a fare with certain features for journeys *commencing in Egypt*; another is a fare with similar/identical features for journeys *commencing in Turkey*; and ditto journeys commencing in Indonesia or Australia.

Customers in each market (Egypt, Turkey, etc) will have different abilities to pay (based on income) and different willingness to pay (based on competition for the same product) those fares. So the prices for each market differ to take that into account.

The assumption behind the fares is that fares commencing in each market will be bought pretty much only by residents in that market. However, that doesn't hold in practice any more (it might have historically, pre-WWW), as you can find out on the BA board and their ex-LIS fares. So if you want (and if you can arrange the payment & ticketing) you can usually buy an ex-Egypt fare, however -- you have to commence it in Egypt, which means you have to get there on a separate flight, not part of the Global Explorer ticket. And ditto getting back to your origin afterwards.

For some, the saving outweighs the time & inconvenience involved in doing this; for most, I suspect it doesn't.