Other responders have examined the relative value of each stat in 5e. However, there could be other reasons for not including Cha and Wis items, namely balance for multiclassing spellcasters.
The reason I clicked on this thread was to see how powerful a Warlock 2 dip could be. With a Charisma equivalent of Gauntlets of Ogre Power, or Belt of X Giant Strength, a character could use eldritch blast, perhaps the best damaging cantrip in the game, almost as powerfully as a Warlock of the same (combined) level(s).
Currently, characters multi-classing into the wizard class could pick up a magic item that allows them to use the class at close to maximum effectiveness thanks to a magic item. If casters could be reassured they could dump their casting stat (or keep it to the minimum for multi classing) and obtain a magic item then any optimization focused build would involve raising Con and Dex as high as possible, taking any relevant feats, while ignoring increases to their casting statistic.
It would completely alter the feel of magic using classes, and specifically multiclassing, in 5e.