I haven't played the IJ game or seen any details about its DLC, but DLC can sometimes be accessed before the main game is completed.

It could potentially be like the Dark Souls 1 DLC, where you can enter the area at any time after a certain point in your playthrough. You can enter Oolacile after you defeat the Hyrda in the Basin and the Crystal Golem in the Duke's Archives. This can be completed at various points in the game before you finish the game.

People do all the time and it makes no sense to me.

I assume it's people who are highly motivated by hype and the community conversation to play something while it's in the zeitgeist, the same as people who want to skip stuff to play story games that are direct narrative sequels without bothering to play anything before it, presumably just because it's popular and catches their eye.

Probably the same drive that keeps pre-orders and day one sales so high, despite it pretty much always being a better idea to wait a year or so for sales/updates/etc.

I felt the same way about Deathloop. These types of games just aren’t for everyone.

I feel the sane way. It had very uninspired, well trodden gameplay (with some aspects quite poorly done) along with a passable story.

The highlight for me was just taking in the scenery in the jungle section, almost felt like virtual tourism. But I was hoping for something more original, since I enjoyed the first wolfenstein game from machine games quite a lot.

Overall I didn't feel it was worth the price, even on sale.

Thing is, most of the discussion online is guided by reviews from major publications. If someone like SkillUp says the game is good then there will generally be a positive discussion about that game. Personally, I haven't played it nor do I ever really plan on playing it. Something about it just doesn't catch me eye the way certain games do, I feel like I'd have a similar experience to you if I did play it.