Good morning,
all published Apps available in the Tenant are shown.
Typically, they should all be published on the application service (AS) where the tenant is in mount; all AppSource extensions are published in the ASs and these are visible as installable in all tentants.

If you create a new Sandbox or a production environment, you see all the Apps available in Sandbox (ex. In Sandox Business Central Release Wave2 SaaS)

Would it be possible not to show them?
Customers ask us what they are and what they are for, which is quite annoying for the partners. Better not let them see, at the limit is the partner who shows the addons to the customer.

Roberto Stefanetti
Ideas Administrator

Thank you for this suggestion! This is now implemented in Wave 1 2020 update of Business Central. 

Best regards,
Business Central Team