Why is this site not known by whois?

I've been receiving author promotion spam - and these sites all seemed very like each other so I figured I would check them with a whois check - So the first site is https://bookois.com/

I went to whois.domaintools.com and searched https://whois.domaintools.com/bookois.com it says

Whois Record Not Available This domain is not registered.

and asked me if I wanted to buy it?!?

It seems the domain is being served on cloudflare, but how are they doing this and why?

The next site is https://apenbok.com, which is registered but no website it says, although it is dereferenceable with one. Hosted on Hostinger International Limited.

The other ones have more info and so while they do look scammy like the others are probably ok.