Some saudis are tall sure, but 99% of you that ive met personally were all skinny, which is weird cause most mideastern dudes here are ripped or buff due to working out, guess when youre rich and spoiled you dont care about all that.
None of what you are saying makes any sense. Saudi Arabians of Arabic stock are first of all among the tallest people in the Middle East and at the same time not exactly skinny but rather the opposite. I don't need to remind you that most are probably heavier and thus more broad-shouldered than your average Iranian. Nor do I need to remind you of the fact that 10% of the Saudi Arabian population are Afro-Arabs and it is common knowledge that Africans/Black people are generally stronger built/more athletic than Caucasians.
For instance look at the Saudi Arabian national football team. Taller and more heavier built on average than ALL other Middle Eastern football national teams.
Lastly the ghetto/gangsta culture that many other Arabs and Muslims (unfortunately) have adopted in the West is foreign to most Saudi Arabians since Saudi Arabians were never immigrants to the West in recent times nor is that culture prevalent in KSA.
Most importantly I suggest to read about the descriptions of the Muslim Arab armies (by non-Arabs) and the Arabs of modern-day KSA from 1400 years back and forward and how they were described. Most were described as tall and broad-shouldered and as ferocious fighters. Hence them conquering half of the none world and establishing the biggest empires seen in human history at that time until the short-lived Mongol Empire and the British Empire not long ago.
Wrestling and other martial arts were obligatory for most Arabs back in the day. Wars were very common hence most Arabs were highly skilled warriors. In fact infighting/tribal wars were the biggest hindrance for expansion back in the day until Islam came which united the people for the first time in recent memory.
Central power was a foreign word. Every Arab wanted to rule himself and there is an Arab saying (due to the prevalence of Arab families and titles in abundances that most Arab tribes or families held at least once in their history) that "every Arab claims to be a king". Don't know how to exactly translate t into English for it to make sense.
Anyway everyone saw what happened when the Arabs got united for once and what that meant.
But yes, of course many, due to being affluent, are not doing much physical activity and are thus getting OVERWEIGHT.
It shows that you live in Iran? When have you met any Saudi Arabians in Iran?