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.

Other than that, maybe ads

Because they also offer free DNS and email. There are no ads.

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.