Chaosmancer
Legend
Well the lore also said hobgoblins created common goblins and that process was magical. So it is also valid to think they did the same with half orcs.
And its not like anyone knows the true origin. There is no canon origin for 4e POL half orcs. They are just a race with a mix of orc and human traits.
But to WOTC, Half-orc were the PC orcs and Orcs the NPCs orcs. With the rules changes, WOTC has no idea how to differentiate them, refused to create one, and more or less gave up.
Or, they looked at their four options.
1) Point buy races that completely destroy the idea of consistent races and would be a nightmare to balance
2) Making over a thousand unique races for every single mixed race combination
3) Just keep things the same and say that only two types of mixed race people exist.
4) Make the mechanics not matter, and just keep it as simple as possible
And they picked the option they felt was best for the core game. Because options #1 and #2 are not great options. They are a massive undertaking, very likely to cause more problems, and far too easy to break.