Old wallpaper extras have some standards . They comes in too many resolution and max resolution is always 1920x1200 . That's perfect . Nowadays I saw too many games comes only one wallpaper or only one resolution . What is the reason behind it ?

It takes less manpower to only create one. I'd guess cost pressure and lack of personnel.

It seems cheap work :S Why we love GOG ? Because quality of extras . In old days I bought some games only for Extras . Because I have already disc version or on other service . But nowadays they are nearly worthless :S

well at least the extra's are free. Some publishers have the nerve to charge you for costumes, wallpaper, in game music...

Also more important thing I don't know "Max Resolution" now lower than before . 1920x1200 wallpapers are a lot better than 1920x1080 wallpapers

Yes, you're right, but even for this you need somebody to do it and there's a long ToDo list at GOG's. In my experience, the staff is pretty occupied and hence forced to prioritize. Nothing unusual and in my opinion wallpapers aren't top priority, as I can easily make dozens of them with screenshots myself (or if you will, scale the one that comes as an extra).

I missing old wallpaper extras nicely crafted for all sizes . Now they comes with only one size or they comes cropped :S It seems weird .

For me a single best-available resolution would be enough.
Resizing, even with Paint, is a procedure of just few seconds..

Ok that explains everything I think fair enough .

I haven't tested it but Windows and other operating systems presumably have an option to scale a wallpaper image and could likely take the large image and scale it after the fact themselves down or up to the native resolution.