This from Amazon’s help pages:
Amazon has determined that it is in the best interest of the customer, sellers, and company to hide (or suppress) listings that do not meet our standards. We will suppress a listing from search and browse when the listing detracts from the customer shopping experience.
Reasons for suppression include missing information or incorrect or invalid values. The listing will be suppressed from search and browse until the listing flaw is corrected.
We suppress listings without a main image in all U.S. categories, except the following:
Automotive Parts and Accessories
Industrial & Scientific
For more information about image requirements, see Images.
We will suppress listings without a value for the Category (item-type) field in all U.S. categories, except the following:
Grocery & Gourmet Food
Health & Personal Care
Shoes, Handbags & Sunglasses
Even when suppressed, a listing will continue be shown in your seller account. You also can locate it on Amazon.com by typing the exact ASIN into the search box or clicking the ASIN link in Manage Inventory.
Note: Suppressed listing alerts are updated every 24 to 48 hours. Your updates can take 48 hours or more to appear on Amazon.com. Alerts usually disappear from the Suppressed Listings tool within a few minutes after saving your updates. However, alerts can remain on the Listing Quality and Suppressed Listings Report for 48 hours or more.
Fixing Suppressed Listings
To download a Listing Quality and Suppressed Listings Report, follow these steps:
Under Inventory, select Download Inventory File.
From the Select Report Type drop-down menu, select Listing Quality and Suppressed Listings Report.
Click Request Report.
It can take up to 45 minutes for this report to run. You can leave the page while the report is running.
When the report is complete, a Download button will appear in the Download column.
Click the Download button.
To fix suppressed listings in Manage Inventory, follow these steps:
Go to Manage Inventory.
Select Fix Suppressed Listings in the left navigation pane.
Fix Suppressed Listings is visible only if you have suppressed listings. If you do not have any suppressed listings, this option will not be visible.
Select a viewing option, such as All Suppressed Listings, or a subset, such as Image Missing.
Click the Actions link for a listing and select an option, such as "Manage Product Images" or "Edit Details (Fix Listings)."
On the Amazon Product Summary page, select a tab with an alert indicator.
Suppressed listings are indicated by a red exclamation point. You may also see Quality alerts, which are indicated by a yellow triangle.
After you have resolved all alerts for a listing, click Save and finish.
Note: If you use feeds to add or edit your product listings, you can still use the Suppressed Listings tool to make changes. However, you must also update your feed files or the changes you submitted through the tool may be overwritten by subsequent feeds. To avoid duplicating your work, download the Suppressed Listings report and update your feed files based on the report.
For Pro Merchants
If you have a Pro Merchant account and use the “Add a Product” tool, you can use the Suppressed Listings tool to find and fix suppressed listings.
To download a Suppressed Listings report, follow these steps:
In Inventory, select Download Inventory File.
From the drop-down menu, select Listing Quality and Suppressed Listings Report.
Click the Request Report button.