The default values for catalogs saved are taken on the App Create purchase requisition.
However the same values are not considered in the App Manage Purchase Requisition Professional
The App Manage Purchase Requisition Professional doesn´t read the default values about catalogs assigned per user. This App is not understood as an app assigned to one only user but as a collective way to Manage PRs.
The App that is designed for specific users that reads the assigned catalog is Create Purchase Requisition App.
This is the standard desing, you need to use the App Create Purchase Requisition to get the default settings per user.
Please see the KBA 2838428 in case you want to create a Feature Request.
KBA , MM-FIO-PUR-REQ-PRF , Manage Purchase Requisitions – Professional , Problem