Old Photos and how common was the process

My wife and I were wandering through an antique shop last evening killing some time when I came across a batch of old silver photos, circa 1900, as I have in other antique stores on other occasions. It's pretty common to find these types of photos by the box full. Must be every town had no fewer than 50 photographers in it taking pictures at reasonable prices people could afford, that so many survived to today.
Once in awhile I'd even come across some Dags for sale. Although I don't ever recall coming across any Albumen prints, or any of the other exotic alternate process types. I can understand why glass plates would be so hard to find. Yet you'd think that some of the processes that were put on paper could be found. What about pt. / pd.?
Why is it that since I have an interest in Albumen prints that suposedly last for generations, that the only place I can find them is in a museum. How come I can find some in a box tucked away in some antique shop somewhere? It would be kind of nice to have several for reviewing and reference as a small collection as kind of a target to shoot for.
Were some of these processes very short lived or too expensive for the common working person to afford? Were some strictly experimental in nature?
Would anyone know of any good book titles that outline the history of the photograph, the different processes and how common they were in use?
It's so interesting to read all the posts on this site today concerning the different processes of long ago that seemed to all but have vanished!
As always, thanks for your input.

I'm not exactly sure why these would be so rare, but it seems to me that ceartain proceses (platinum / palladium albumin, etc.) were used for more artistic purposes than for everyday printing.

I've run across cyanotype postcards on several occasions in antique shops and flea markets. And I've also found a box of the unused cyanotype postcards once. I think it was a common amateur process at one time. I've also seen some studio portraits in fancy cardboard mats that I'm sure were albumen prints. I think they are more common than your experience indicates, at least round these parts.

Joe

Joe, thanks for the encouragement, I'll certainly keep my eyes open.
I'd like to make a correction to the 11th line of my post above which should have read:
How come I CAN'T find some in a box....

According to the announcement for the albumen workshop I'm taking next week, albumen was "the most dominant printing process from the 1870’s to the 1890’s." That's not an authoritative source, but it might help in narrowing the period in which you would find albumen prints.

I think there might be regional and national differences as well?

I have had no problem finding albumen prints locally, not collodion paper prints or silver gelatin POP prints. I had to go a bit further afield to find cyanotypes (France) and Pt prints (Canada)...

The biggest find I ever had (not that I look for albumen prints that hard) was an album that had been compiled by a clergyman in East Anglia, England, as he had tried to teach himself (I presume) the wet-plate process and albumen printing. Text references dated the pictures to 1857/8. The prints in the album were on very thin paper, which I believe is the characteristic of albumen prints, along with a very smooth fine-grained surface. The prints had deteriorated quite a lot despite being kept in a book, but they had been made by a self-confessed incompetent who in fact concluded the book by saying he found the whole process too hard and was giving up! In view of the poor condition of the pictures, which meant they needed urgent conservation, and the lack of intrinsic artistic interest in the pictures, I sold the album through an acquaintance to the National Monuments Record (the photographer had made pictures of his own vicarage and church).