Thank you for reporting a bug to Unity.
After reviewing the behavior, we've confirmed it aligns with the current design and intended use of the feature. We understand this may differ from your expectations or workflow.
As it stands, only the initially added custom Build Profile is automatically activated. Any subsequent additions are not, by design. This allows for multiple Build Profiles to be created without having to wait for a reload to happen in between each addition.
We will close this case as 'As Designed.' If you have feedback on how the feature could better meet your needs, please let us know - we value your input and consider it in future improvements.