There was a large surge in sales as Digital replaced Film. I believe it was fueled by economically priced DsLR's and there was no cost in processing film. Many who never had a film camera bought in and it created the spike. Over the years the fall off is reflected in this forum. Back in the day this was a busy place, there are just a few regulars left.
In your graph though we should see an uptick in mirrorless when DsLR's are no more. I would have thought it would have been noticeable already.
Phones are getting better. I shot the X-mas present opening this year with my new iPad rather than the R5. Results were fine for what I was doing.
Possibly only people using ILC's in a few years will be those of us who use it as a specialty item rather than a tool to shoot family events.