In Windows 10, changing desktop icons does not always show the full gallery of icons. WhY?

1. Usually, on the desktop I right-click on the icon I want to change.
2. I click on PROPERTIES
3. In the figure that now pops up, showing the icon I want to change,
I click on CHANGE ICON
4. The gallery of icons now pops up
5. I choose an icon from the several ones in the gallery.
6. I then hit APPLY > OK

But why does the gallery sometimes show only a few icons, none of which I
want to choose?

Many thanks for your help.