It’s an interesting correlation but I tend to wonder if it has more to do with counterfeits on Amazon than sense of smell?
Are you claiming that counterfeits are affecting all three? Or that there are enough counterfeits in at least one of them to cause the average to drop so substantially? And that is a more likely outcome than covid affecting a substantial portion of the population causing a drop in reviews?
The reply this tweet thread is based on is from the seller's own website themselves seeing a large increase in negative reviews from customers that state their candles have no smell.
I feel jumping to conclusions about a rise in counterfeits is unnecessary.