I think they're pretty different use cases. LibreOffice Base and Kexi are desktop database frontends focused on local databases, while Mathesar is web-based, self-hosted, can be connected to a remote database, and built for multi-user collaboration.
Far too technical for the target audience, who has never heard of a "linux" and doesn't care about cost, software freedom, the petite tyranny happily imposed by corporations, etc, they just want it to "just work" on their smartphone browser.