they should purge accounts that are inactive. be it 1 year or 5 years they could easily just make an arbitrary period. I know in the past people would create new accounts to subscribe but never use the account after that. fake emails are easy to come by.I'd love youtube to do a purge of content maybe based on engagement. It must cost them so much to store so much dead content. His subscribers vs views is appaling engagement.
Or purge youtube accounts that are bots or have been inactive for a certain period
and the bot subscribers that people buy should be relatively be easy to filter out.