n-gramming Collecting

Google Books n-gram (https://books.google.com/ngrams) is an interesting tool, even if it does only go up to 2008. But it has some telling results. Look at this (detectorist/metal detectorist):

So, according to this, the topic began to be talked about using the term 'detectorist' rather than 'treasure hunter' around 1986/1987. Here are some more (the word looter however could mean a lot of things other than one who raids archaeological sites):

and this one:

but what about this (in a different timespan)? Why does it abruptly start about 1963 and remain at a low level until 1984, and then suddenly take off like that? Why is there that downswing 1999-2003?

('ancient art collecting' remains pretty stable and much more prevalent over the same period).

Here's the bottle collecting/digging fashion shown (and relic hunting):

Note that I have conflated US and UK English, you can separate them out and the patterns differ from each other.

I am not sure if these 'mean' anything, but they are of interest - and provoke questions.