To answer the op's question............ IMO, yes, and I also think vid1900 is spot on!
I entered the hobby in '88, advertised to buy pinballs in a pennysaver type mailed publication. I used to get 30-40 calls a week with people wanting to sell their non-working pin out of their basement. I was able to pick and chose.
By '95 I noticed I had to hustle if the machine was desirable as by then, there was some local competition.
By the early 2000's I had to hustle to ANY machine I got a call on as I noticed huge competition by way of an ever-growing hobby, and also a bunch of flippers in the area. The 30-40 calls sank to maybe 1/2 dozen, if that many.
By 2010, I noticed after dwindling supplies, a few recessions, etc, most general-public-type sellers were plugged into the internet, did searches and attached unreasonable prices on their broken down pinball, (and anything else), rotting away in their basement that could be worth a few bucks. Done with flipping and happy with my collection, I decided to hang up the hand truck.
Are the desirable titles gone? I'd say so. The hobby is no longer in it's infancy, and those great Wms. Games of the 90's are at or approaching their 20th birthdays. Finding one, or a classic EM reasonable these days is usually considered very lucky.