I just checked the old BG games real quick and found out that in those games Halfling also has max 17 WIS, not 18 like all other races, at character creation (standard is min 3 and max 18). Other races have similar min/max on ability scores. Dwarf has max 17 CHA and 17 DEX. Elf has min 6 DEX, 7 CON, and 8 CHA.
I think it makes sense, if you think along the lines of "on average the typical halfling is less wise than a typical member of other races". From a certain angle, it's also not that unreasonable to argue that, under the exact same circumstances, a halfling can never be as wise as a member of other races. A human will always be more charismatic than a dwarf, under the exact same circumstances (same clothing, same knowledge, same social skills, same self-buff magical effects, etc.)
