That's a feature, not a bug. Literally anyone can own an instance.
You can install Open Source software like Mastodon or Pleroma on a cloud service like AWS.
You can get a turnkey server from https://masto.host/
Or you can join a cooperative like social.coop or cosocial.ca, and have shared ownership with other like-minded people.
GNU social JP is a social network, courtesy of GNU social JP管理人. It runs on GNU social, version 2.0.2-dev, available under the GNU Affero General Public License.
All GNU social JP content and data are available under the Creative Commons Attribution 3.0 license.