First off I'm not on the redesign team BTW so haven't been as involved in this analysis enough to adequately answer your question and also my statement is one that you can quantify as such.
But the reason I stated it is that A: it was a heavily requested feature B: comments regarding infinite scroll have been weirdly positive (contrasting my point in another reply about most comments are from very strongly opinionated users) and C: usage statistics ie I can assure you when compared side by side people make more of the equivalent page turns. Personally I like both methods but infinite scroll was a clear winner for us.
But why is there no static fallback for when some script doesn't work? BetterReddit allows me to use both methods concurrently on the old design, why is the new design limited to a method that doesn't work for me?