Where are the 6000 Items

in the Imperial Palace Gallery, I read that there are 6000 items there and thinking I was getting a heck of a bargain (since it was free and the Tokyo museum in Ueno cost money) I gave up going on my Mt. Fuji tour (only one last day left so can't go) thinking I would be there for HOURS and it was only about 5 minutes. Asked around and there only seemed that small galley, and no other, do they just rotate the stuff or what, so disappointed.

Sannomaru Shozokan is basically a storage. The storage area is 1000 sq meters, while the museum area is only 160 sq meters. Now, they store 9800 items, not 6000. They plan to expand the facility, but still, the storage space would be 1800 sq meters, while the museum space would be just 360 sq meters.
https://ja.wikipedia.org/wiki/%E4%B8%89%E3%81%AE%E4%B8%B8%E5%B0%9A%E8%...

When I visited there, there is a very long queue, so I just skipped it. Your information is very valuable for future visitors, at least.

Tokyo Museum is only Y620, so not so much, but even there they rotate items and the displays change. Certainly they have more than enough to see for a couple of hours.
Many museums I know of have much more stuff than they can display. Only a few small niche places I sometimes visit have everything on show. If the Palace museum only has 100sqm, then they would only have a very limited display (maybe similar to the tiny sumo museum at Ryogoku - no space to display much at any one time).