I'm kind of surprised people thought anything else would win.
Last year we voted in Bloodborne (23 critic, 8 reader GOTYs) over The Witcher 3 (169 critic, 88 reader GOTYs).
The prediction formula has been "Biggest Sony Exclusive, unless they're all bad, at which point Biggest Nintendo Exclusive" for half a decade now.
This year should be Horizon, unless it gets a poor reception, at which point it will be Zelda. Edit: AniHawk reminded me that Persona 5 is PlayStation exclusive. It will actually be that.
Next year will be TLOU 2 unless it gets delayed, otherwise God of War.
I don't think Bloodborne being exclusive really play a role in it wining, It was just robbed everywhere else. Though being serious if it was multiplat it would have just won by a greater margin.