Referring to this post:
Tag suggestions are only user-specific in Portal for ArcGIS - meaning there is no mechanism for users to see other users' tags in their Enterprise Portals, and be able to choose to keep their tags consistent with other users, and thus their content more consistently discoverable!
Alternatively, portal admins could be given the capability to setup a standard tag library during the installation of Portal that would control the suggested tags all users would see.
This is a huge oversight in my opinion on esri's part for Portal.
Even the tags on this idea board supports showing suggestions previously input by other users!
