[object-a]

An experienced DM can of course let their players create whatever character they want, but a less experienced DM might be concerned about balance/fairness/implications of bending the rules. By creating an alternative, flexible rule for ability scores, a table can feel confident that the characters they build are still balanced.

> The changes WoTC made are bad, and make everything less fun and more generic. Their intentions were good, but what they've done really isn't helpful or good at all.

As you said above, the DM and table can agree to whatever constraints they want for the game, including using the old ability scores.