This is the intended behaviour: tag discovery is provided from vSphere onto Aria Automation for convenience, but otherwise tags are not synced between the two platforms.
The rationale is that the tags could have an impact on vCenter/Automation if they are carelessly "cleaned up" by an admin on one side and then synced to the other.
There is a feature request created for the ability to configure this update timer. If you are interested in this, please contact Broadcom Support referencing this article number (417391)
Creating and managing Broadcom support cases
In current versions, it is possible to create a custom process to delete tags from both the Automation and vSphere sides, for example:
An equivalent Add Tags workflow can be used to create tags on vSphere, as this will be discovered and applied in Aria Automation.