Even if that part is true, you have the consider the raw numbers: chances are that way more people played TW3 than BB. People with only a PS4 could have voted for both games, but people with only PC/Xbone could only have voted for TW3, so TW3 definitely had a higher chance of appearing in way more charts than BB, hence skewing the votes in TW3's favour by "brute forcing" results from players' count alone.
I get what you're saying, but I don't think that the votes from PC/Xbox users are as skewed to TW3 as you are thinking.
1. There is already a low volume of exclusively PC/Xbox users
2. Just because they don't own a PS4, doesn't mean they've even played it. There are some PC gamers who mostly play indies or shorter games here. Xbox fans aren't particularly huge on RPGs in general apart from Bethesda games and Mass Effect like many PS4 owners would be. This pool of voters isn't that large to begin with. (PC/Xbox exclusively)
3. Can we be sure about more people playing TW3 on GAF specifically? (at least of those that took part in the vote) It certainly sold much more overall, but as I stated, FROM is in an exclusive club with ND in terms of GAF passion. It was also the first exclusive that made the PS4 feel "worth it" to many here so it was widely played and the OTs and DLC OTs are significantly longer than those of TW3.
There was more volume of Bloodborne votes, but those who had both in their list ranked them 1-2 in basically equal proportion. I could be totally off on this, but from what I've seen in the OT, many on GAF are still working their way through TW1/2 or intend to before playing TW3 for story purposes. Some are even reading the books. This would probably be more important here than at a place like say IGN. This isn't much of a thing for a new IP like Bloodborne.
It's also a very long game so many might not have been comfortable voting for it before reaching whatever level of completion they deem necessary. It could be that many played it and just didn't like TW3, in comparison to Bloodborne, but the data we have doesn't seem to show that. (47% of those who voted for BB had it as their top choice which is exactly the same number as those who voted TW3 as their top choice + the above data referring to their ranking by those who had both in their lists) Again, I could be wrong, but I don't think that users on a site like GAF conform to the same type of purchase choices of a regular site.