The request is already under review. See this request: https://microsoftteams.uservoice.com/forums/555103-public/suggestions/19340470-merge-consolidate-channels
This is something that is really needed. Two people can create the same team without the knowledge and than they suddenly finds out two teams exist with same purpose. Now they phase the challenge of merging the conversation history, files, content, etc.
This request is now being reviewed by the feature team! I’ll keep you posted as to the future decision.
The lack of support might be due to the missing support in Microsoft Graph for Conditional Access, which is need for some parts of Microsoft Teams.