Why would it need to make money, it's just a registry of information and a small about page with a list of entries. It probably runs on sqlite on a single $5 VM. Or a single db.
It looks like DNS is just shared CloudDNS, and email is limited. From the FAQ:
How reliable is dot.bs DNS hosting?
dot.bs is backed by ClouDNS. ClouDNS serves over two billion DNS queries per day, so I can confidently say your DNS is in good hands.
Do I really get free email?
Yes! In order to make this possible, there are some limitations.
A maximum of 5 email accounts per domain (unlimited domains)
A maximum of 5 outgoing emails per hour, per account (to prevent spammers)
A maximum of 75 MB storage per account
If these limits are a problem for you, please reach out and we can figure something out.
Other than that, maybe ads