Thanks for the answer. I do understand the issue that there can be a missuse of the "free tenants". As other mentionded, I will also pay for my subcriptions and like to add tenants as needed.
I'm using the DEV Tenant with e5 licences for my studies and an VS subcription for Azure (as well as pay-as-you-go) to save my wallet :-) and I wanted to "merge" my old one to the new one. This is not longer possible
Not everybody has to opportunity to build every service in Azure on the companys' bill.
So very appreciated if Microsoft can reopen the ability to add tenants on the credit card bills.