Other people can run AppViews too (that operate over the same or different data). There are just less people doing that than hosting Mastodon instances partly b

Other people can run AppViews too (that operate over the same or different data). There are just less people doing that than hosting Mastodon instances partly because it's much more expensive to, because some of the benefits of hosting a Mastodon instance can be obtained much cheaper through running a PDS server, and because AppViews doesn't serve the same exact social role that Mastodon instances do. (Mastodon has every instance be a semi-isolated community, so Mastodon instances are often made for the social purpose of running a semi-isolated community. Bluesky users expect a global timeline that's not partitioned by server instances, so it doesn't get many people running AppViews specifically for fostering semi-isolated communities. People on Bluesky who want to foster semi-isolated communities tend to use features like custom timelines to do so instead.)