This is assuming though that Sorceror's are just casters. Presumably the sorceror would want a decent AC and be able to use some of their skill proficiencies as well. Depending on your stat generation rules, it is not uncommon in games to have spellcasters max their spellcasting ability score fairly early on. And despite the high CON, the sorcerer would still only have a d6 as their HP dice (which would make hit dice conservation interesting on short rests as well). Also - sorcerers are already proficient in CON saves, so it's not like there's a huge difference between a +2 from CON or a +5.

The main convincing argument I've seen against this is abuse through multiclassing, but then again, since CHA is such a common spellcasting ability (and is useful out of combat) Sorcerers are already an easy multi-class dip for spellcasting (especially so martial classes can use meta magic to cast a spell as a bonus action and still attack during their turn).

TL;DR - I understand the issue, and agree CON as spell casting ability would make them more powerful, but I don't think the arguments against are as convincing to me as they seem for other people.