You can for yourself, hosting a large instance for others does require time, financing, a legal entity (if for nothing else, liability purposes). Most people are much more likely to use what is already there unless they have an itch to do it themselves.
Mastodon is a non-profit that also hosts the largest mastodon instance, ultimately I think there will be a ton of small hobbiest instances and a few big ones - they should preferably be run by non-profits to help avoid the current Reddit situation (more like other open source projects).
Beehaw defederated from some of the larger Lemmy instances due to problem users and limited moderation abilities (Lemmy as a platform, limited staff). As one of the larger Lemmy instances themselves and where many Reddit folks went, this rubbed some people the wrong way. Beehaw has a specific idea about the community they want and are proactive in protecting that vision, I don’t know how this makes them “corporate” but there you go.