Domains are used for more than just webhosting. The owner could have email accounts, etc, that use the haiku.org domain that they don't want to switch to another less recognizeable name.
Starting Nmap 7.80 ( https://nmap.org ) at 2022-01-01 14:17 CST
Initiating Parallel DNS resolution of 1 host. at 14:17
Completed Parallel DNS resolution of 1 host. at 14:17, 0.00s elapsed
Initiating Connect Scan at 14:17
Scanning haiku.org (35.213.168.88) [11 ports]
Completed Connect Scan at 14:17, 5.00s elapsed (11 total ports)
Nmap scan report for haiku.org (35.213.168.88)
Host is up.
rDNS record for 35.213.168.88: 88.168.213.35.bc.googleusercontent.com
PORT STATE SERVICE
21/tcp filtered ftp
25/tcp filtered smtp
53/tcp filtered domain
80/tcp filtered http
110/tcp filtered pop3
143/tcp filtered imap
443/tcp filtered https
587/tcp filtered submission
993/tcp filtered imaps
995/tcp filtered pop3s
3306/tcp filtered mysql
Read data files from: /usr/bin/../share/nmap
Nmap done: 1 IP address (1 host up) scanned in 5.06 seconds