It's a new item, Thresh is the most popular support meaning people are much more likely to fall into buying noobtrap items instead of actually doing the math and finding out what's best for what situation AND who cares if 1 out of TEN Thresh's build it in its first week instead of getting a Frozen Heart or whatever it is you'd prefer him to be buying because obviously build fluidity isn't good for the game. Not to even mention the fact that LolKing's stats don't even make sense, Thresh is played 55-60k times a day on average in just ranked and yet Ardent Censer's 10% is 300 picks, which also brings up are they looking at normals or rankeds?
Seriously though there's no point in continuing this thread of comments since you're so steadfast in your opinion that "tanky" supports' only role on a team is being a meat shield and if they dare even spend a drop of their gold on something other than just tank items there must be something seriously wrong with this game. You're not supposed to try and round out your character with your item choices, no, you're only supposed to focus on one thing, in this case tankiness, and have that in every single one of your purchases and if there's any reason whatsoever to not do that then Riot has obviously failed at making a good game for providing additional choices for build fluidity. Honestly, why aren't you flipping out about Talisman being the #2 item on Thresh before even boots 2, it gives no tank stats at any point and it's whole purpose is being a gold sink for team utility, something you're obviously very against a support buying.