And why does God focus His efforts on the Middle East alone? Wasn't God aware that people lived in other areas of the globe?
Because we're talking about the OT, which deals with Israel: a group of people in the Middle East.
This must mean the first topic you brought up, 'slavery', is then considered moral by God forever? Care to discuss? Slavery continues to be a 'custom' for some. Not just in the "middle east".
No, it doesn't. Even though the OT doesn't say, "do not own slaves," it has several books that approve the story of a group of slaves escaping from their masters. There are also commandments about marrying a widow, so that she would not end up penniless, about releasing slaves after a certain period of time, and about treating aliens well. In the NT, we have St Paul advising Philemon to treat his run-away slave well and in a different place he writes:
Gal 3:26-28 In fact, you are all sons of God through faith in Christ Jesus. Indeed, as many of you as were baptized into Christ have been clothed with Christ. There is not Jew or Greek, slave or free, male or female, for you are all one and the same in Christ Jesus.
This may be bad news for Jews, slave owners, and men. It is certainly very good news for Greeks, for slaves, and for women.
Why would such a God be so 'weak', as to not mention His disdain for the five topics above, when many other 'customs' of the Middle East were said to be a sin' all along? I'll answer preemptively... What's more likely...? A) God asserted such commands. B) People asserted such commands, and passed them off as God pronouncements
If the Bible says to treat slaves like brothers, this is revolutionary. Slaves treated like brothers are no longer a slave. Indeed, they're better off than many employees in this day and age. Still, the Bible doesn't say, "Do not own slaves." That would be like telling you, "Do not use gasoline, it damages the environment." Slaves were the engine for the economy, you need a source of energy to drive the economy. We need a different source of energy to be able to not use gasoline. And God ultimately gave the world the technology to wean us off the unjust source of energy.
I read that the ratio of free people to slaves in ancient Greece was 1:5 or something like that. You can't change that kind of system overnight. It takes time and wisdom / technology.