When using FT as a resource for topics completely new to me, I browse in Private mode, not logged in. If infinite scroll, in the manner it is performing for me, existed when I first started reading FT (over ten years ago, I think), I probably would not have read more than a few pages in my entire life.
It's impossible to keep track of where I am in reading a thread. Sometimes new posts appear at the bottom, sometimes I get the links for other pages, I click an earlier page or a later page, and end up reading stuff I've already read, even if I've never been on that particular page before. I'm in the middle of reading a post and it suddenly disappears from view, and I can't figure out whether it moved off the top of the screen or the bottom.
Even knowing the tremendous potential value of the information on the site, I'm too exasperated to keep trying to read about the topic I want to explore today.