AMEX has been sending out requests for additional reviews over the past few weeks. I received mine a few days ago.

This might explain the recent increase in review volume.

Further, I would add that unprompted reviews tend to skew overly positive/negative, and it looks like most of the unprompted reviews over the past few months tended to be negative in light of the devaluations.

But since these recent reviews were in fact prompted, it would make sense that they would tend to be more mixed rather than just negative. I know that I would have left a 3-4 star review, since the card is still a great value for me even with the recent devals.