I suspect the growth through the 2000s was more related to the internet causing easy dissemination of information, but it is interesting to see the large spike around 2007/8 and then a steady decline in sightings reported since.
A big trend of sensational cryptozoology cable TV shows started around that time too.
I've known two people (a family member experienced in the woods and a close friend) who have had encounters. Not like "maybe I saw something in the bushes" encounters either. I don't think either of them reported them anywhere that would have ended up in this data set.