Private Channels should not create a site collection
Creation of site collection for private channels is not practical. Office 365 considers it as a new site and you came across to references of this new site everywhere. This was not the expectation. Private Channels should just be folders within the main group site as it used to be. You just created sub-groups, not private channels!
This is a huge problem with this implementation. The docs say it's for security but we all know Teams could set the SP security to match the users added to it. The way it's implemented ruins our ability to use this long-awaited feature. Also, with hundreds of teams having to separately sync perhaps hundreds of private channel sites using OneDrive is impractical.
Anna Zhuchkova commented
Definitely support that! We have several settings / permission for support which we use within the provisioning of new sites. For private channels you should just set different folder permissions, there is no need for a whole site with one doc library and again one folder.