In BG1&2 humans got nothing.
(Actually got access to dual-classing, but that was both OP or weak as)
+1 to all stats interacts really well with point-buy; you can get +9 total modifers for a strong overall character. You could even get 3x 16s for a strong but unbalanced build.
It also models that only exceptional human heroes can match archetypical demihuman heroes.
