Because Bioshock released then and a new IP has always more chance of becoming GOTY.

Wasnt Overwatch GOTY 2016?

Well, the link is right there, that's not how "every year" has been.

Witcher 3 decimated the nearest competitor.
Dragon Age more than doubled the closest game.
Last of Us almost doubled GTA V.
Walking Dead beat Journey by over 15.
Skyrim by over 100.
Red Dead by almost 20, which it being that close is almost as big a travesty as Dragon Age "winning" one year.
Uncharted 2 shat all over Batman.
Fallout 3 more than doubled GTA IV, which deserved 0 GOTY awards.
Bioshock barely beat Mario Galaxy, I can only assume they didn't include these reader votes at that time.
Oblivion barely beat Gears.
RE4 obliterated everyone else.
Half Life 2 almost doubled Halo 2.
KOTOR almost got more than every other game on the list combined.

So this is actually the only time a game has gotten less critic GOTY awards but still been the overall GOTY, thanks solely to reader polls. So yeah, it pulled ahead thanks to reader polls :) Not trying to say U4 doesn't deserve it, I couldn't care less for either game, was just surprised critics liked Overwatch more.

yep, a good reminder of why third party support is really important

Outside of PC.

@OP

Sony consoles always succeed?.. What definition of success are we using here?

I don't think this site has always included reader polls/votes, which makes sense imho because it can mess up the numbers. Had they always been included, I think Galaxy 2 would have easily won, I think Bioshock barely beat it. Or it might have been Galaxy.

Either way between BOTW and Odyssey this year I think Nintendo has it in the bag.

That's fine, if one great game per year is good enough for you. I want more than that, at least 6 - 12 of the best games (usually most 90+ titles and a bunch of 85+ titles) per year.

Basically if you wanted access to most of the best games per year, multiple systems have always been the safest bet.

None have been abject failures like the Wii U, for example.  Even the worst so far (we are talking about home console, not handhelds), the PS3, essentially tied for 2nd, not even that far from 1st.

They succeed because they are straight to the point of what most gamers want and that's a console with no gimmicks and investing a lot in new IPs and exclusives. They know that we just want to sit down with just a controller and play games.

You're right on all counts but I'm still looking for a definition of success. 

I've heard some refer to the Dual Shock 4's touchpad as a gimmick.