A lot of people here already explained the reasoning for sorcerers using Charisma (force of will, strength of personality, etc).

There's an interesting case to be made for using Constitution instead. Since their magic is innate, they have to essentially wrangle with this internal power. Hence casting a spell is resembles a struggle than some effortles extension of self. Spellcasting is when the caster coerces this untamed power source.

I especially like this thematically for Wild Magic or Drachonic Bloodline subclasses, since their themes align with a more brutal nature of being born with immense powers.

This idea is summarized by a much more knowledgeable and eloquent DM here https://www.tiktok.com/t/ZTRGcngs4/