Why Character Driven Variants?

Okay, rant time.

Why are they doing character driven variants in lists now?
Isn't 40k a "Skirmish" Game. Sure a big character gets into Skirmishes sometimes BUT not typically.

Does Samael really lead all Ravenwing forces? NO. Can't Afford to. Same goes for Belial and Deathwing.

Tell me where in the fluff do you see a Chapter Master deployed with not even a full company. I'll tell you where: No Where. So why is Pedro Cantor with every Crimson Fist?

Examples of where Chapter Masters have deployed:
Blood Angels: ARMAGEDDON
Salamanders: ARMAGEDDON
Dark Angels: VRAKS (a full half the Chapter was there)
Ultramarines: McCRAGGE and ICHAR IV
Space Wolves: CHARYS (retaking the Spear of Russ, 7 Strike Cruisers and a Retribution Battleship plus escorts were the SW fleet)

So why do characters of such magnitude run amok in the game? And why do ONLY THEY change the tactical doctrines of the Army? You'd think that in a small enough of a force that some Ravenwing/Deathwing could deploy, like they do in the fluff, lead by someone not as important/heroic as what is required by the codices.