I don't know why. Yeah Eldritch Blast+Agonizing Blast may be seen as a boring "standard issue" Warlock combo, but ya get 9(10 with Eldritch Adept UA feat) to literally customize your Warlock for a bunch of stuff. Having a good default option for Combat ain't a super bad deal in my opinion. Especially if you don't auto choose Hexblade and it's super awesome ice cream dip And cantrips are supposed to be the "default weapon" for spell casters in 5E since being stuck with a crossbow and no spells was the dumbest thing, my humble opinion so that maybe just me on the topic, to happen to spell users in DND.