1. We want you to be able to get HTTPS certs for these too without having to manage multiple names, but HTTPS cert names go on the CT log. See https://tailscale.com/blog/tls-certs/ and https://tailscale.com/kb/1153/enabling-https/ . So having your email address in your DNS name (and thus the CT log) from the old beta.tailscale.net forms isn't great.
2. We want you to be able to have multiple separate tailnets per org/account in the future.
1. We want you to be able to get HTTPS certs for these too without having to manage multiple names, but HTTPS cert names go on the CT log. See https://tailscale.com/blog/tls-certs/ and https://tailscale.com/kb/1153/enabling-https/ . So having your email address in your DNS name (and thus the CT log) from the old beta.tailscale.net forms isn't great.
2. We want you to be able to have multiple separate tailnets per org/account in the future.