AI might have driven the final nail in the coffin but the one decision which was truly an inflection point was starting a program that would pay for asking X amount of questions. The platform was cool because of people who wrote ANSWERS -- to the point where the original question sometimes became even tangential to the actual answer but you'd learn so much nevertheless. Quora not only ended the top-writer program for those people it started offering monetary incentives for asking the most inane bullshit questions as long as they got the views. It is truly baffling to me how something that holds so much genuine value can be driven into the ground while making decisions left, right and center (and the whole community trying to tell you exactly what you're doing) that destroyed everything of value in the Quora process. The older answers are still there, but the community magic has utterly evaporated.
I guess it's pretty normal for folks who have seen this happening in BBS/Usenet era but regardless of all of Quora's faults (the tone-moderation of the language was always a bit overboard in IMHO but I don't think it led to the downfall -- it was always there and writers worked around it) it is genuinely disappointing to see every successive platform try to build something of value only to falter and disappear because we just can't seem to keep anything good around.