What makes Half-Orcs stronger than full Orcs?


This is something that’s been bothering me for quite a bit now.

If you take a look at the description of the Orc race in Volo’s Guide to Monsters, it states:

Orcs are vicious raiders, who believe that the world should be theirs. They also respect strength above all else and believe the strong must bully the weak to ensure that weakness does not spread like a disease.

However, here’s a description of the Half-Orc race in the Player’s Handbook:

Some half-orcs rise to become proud chiefs of orc tribes, their human blood giving them an edge over their full-blooded orc rivals.

And this is true, when you compare their differing racial abilities:

Half-Orc:

Relentless Endurance: When you are reduced to 0 hit points but not killed outright, you can drop to 1 hit point instead. You can’t use this feature again until you finish a long rest.

Savage Attacks: When you score a critical hit with a melee weapon attack, you can roll one of the weapon’s damage dice one additional time and add it to the extra damage of the critical hit.

Orc:

Aggressive: As a bonus action, you can move up to your movement speed toward a hostile creature you can see or hear. You must end this move closer to the enemy than you started.

Powerful Build: You count as one size larger when determining your carrying capacity and the weight you can push, drag, or lift.

My main question is… Why?

What makes a Half-Orc gain such an in-combat superiority over their full-blooded brethren? The lack of a -2 intelligence modifier makes sense given their human blood, and arguably you could chalk up their savage attacks due to increased intelligence/tactical superiority. But what about Relentless Endurance?

Wouldn’t it make more sense that the race known for its aggression and selective breeding produce units that have tangible combat advantages beyond the heavy lifting and movement bonuses?

It really boils down to two questions for me:

  1. What lore is there as to why Half-Orcs are stronger, both lore-wise and mechanically, to pure Orcs?

  2. Is this historically how it’s always been, half-orcs being superior to full orcs? If so, why haven’t Orcs assimilated sooner with other races, with the clearly more intelligent and stronger Half-Orc tribes obliterating their weaker, pure-blooded opposition?