There was some comment about it. Basically, it's for security reasons. Those who aren't using those features wouldn't expect them to appear (especially sneakily). And those who are planning to use them will figure out what package to install.

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=953529

This was the message from maintainers:

    Networking and all plugins have been moved into
    the keepassxc-full package.

    Feature creep like SSH agent support, browser
    integration, Freedesktop.org secret storage,
    KeeShare pose undue risks for most users.