Mechanically, if the game's mechanics center around combat, it's valuable to havegood for all stats have value both in and out of combat. Otherwise the combat value of characters starts to overshadow the roleplaying value and the game devolves to a pure combat-festbe useful for that purpose. If a stat has no value in combat, then it turns into aOtherwise you get dump statstats that nobody wants, and you may as well not have people pay for itthe stat at all. It's rare, I think, to run into someone who's willing to be ineffective in combat in exchange for being the party face and just let people roleplay that aspect of their characters however they want.
In D&D 4e expanded on, they continued this trend by having multiple classes of varying types that had each ofwith the sixwider spread of primary character statistics asstats (although this made the primary statistic, so it'sstats themselves less distinct). It's possible to createfind a character with one,class that's good for almost any two main stats in the particular role you want to play, or threewhich makes it easier to design a character with particular strengths and weaknesses in almost any combinationmind and have at least one or two classes that cater to that combinationwho can still be useful in a fight.
As far as I know, many other RPGs don't have this problem because they aren't oriented around killing monsters the same way that D&D is, but other systems will still have forms of spellcasting based on force of personality because it's flavorful.