Thing is, at introduction, the Sorcerer and Warlock were dramatically differentiated by their respecitive magic systems. Sorcerers were spontaneous, Warlocks were at-will. Both huge things in a game that had been using "but only 1 time a day" as a fig-leaf to cover how crazy spells were, it's whole existence.
So, 4e gave everyone at wills, and 5e kept them for full casters, and 5e also made all full casters cast spontaneously. So, Sorcerer, Warlock, why are you here again?

For that matter, no-longer-Vancian wizard....