Why Google cache of most Amazon.com pages are desktop version?

[zacsg]

Some background:

1) I guess amazon.com had switched to mobile first indexing long time ago. (cannot be sure though)
2) I think amazon.com uses dynamic serving as the URLs stay the same regardless of device, but different content is shown, depending on you visit via desktop or mobile phone.
3) After switching to mobile first indexing, Google should predominantly index mobile version of the site.

The question: if above are right, Google should index amazon.com mobile pages mostly, and the Google cache of amazon.com pages should be mostly mobile version? But I noticed Google cache of most amazon.com pages are actually desktop version. Any idea why?

Thank you.

[not2easy]

Are you seeing cached desktop content on a mobile device? That might be strange.

[zacsg]

I'm seeing cached desktop content on desktop.

Assuming amazon.com had switched to mobile first indexing, and Google has only one index, I thought we should see cached mobile content even on desktop? On most other websites, I see Google cached content are mostly mobile version (on desktop device), but not Amazon.

[nikhilrajr]

I work in ecommerce. Most large ecommerce websites are still in desktop index.

[RedBar]

I see Google cached content are mostly mobile version (on desktop device),

]
Maybe a stupid question however you are viewing with a clean browser cache and history?

At very quiet times of the year I have seen my ISP's cache not updated but that is very rare.