Why does the Blade Warlock need to wait until 12th lvl to add CHA to damage?

@DnDslut69 @JeremyECrawfordwhy does the bladelock need to wait until 12th lvl to add CHA to damage, when every lock gets CHA to EB at 2nd warlock still gets standard ability mod to weapon damage until then #wotcstaff

— (((Mike Mearls))) (@mikemearls) October 17, 2016