If you know your history of D&D, the sorcerer is supposed to have a limited selection of spells and is able to cast them more often than the wizard, whom, might know more spells but must prepare them in order to cast them.
The sorcerer always have its limited amount of spells at the ready, while the wizard can only prepare a limited amount of spell. This is the fundamental difference between the two.
So the point of a sorcerer is to be "stuck" with its spell selection. That at level up a sorcerer can change his spell allotement is acceptable, but overnight? That's a wizard's job and strong point. This means that on rest the sorcerer becomes way more powerful than the wizard because the sorcerer can now have access to his full spell list while the wizard isn't. The wizard class must still find its spells be it by leveling, buying and copying from other wizard's spell books or scrolls.
This idea of the sorcerer class changing its spell allotement on a long rest is what we call in French a false good idea. This new rule simply makes the wizard obselete. Might as well remove the class altogether as since the sorcerer no longer have its weakness, no need to make a wizard. Versatility is now on the sorcerer's side too.