Currently there is no convenient way for end end user who has purchased software from an ISV to install a side-loaded MSIX package machine-wide (for all users). Software is often licensed on a per-ma...
Either installer executables created with NSIS, installed with elevated permissions, or MSI's created with WIX, installed with the AllUsers feature enabled.
In both cases, a user with elevated permissions would install the app for all users of the machine. In some cases the separate user accounts may even refer to the same person and user accounts are used for privilege separation.
But in most cases its an admin that physically goes to the machines (or uses remote login) and actually installs the software.