There is value in government agencies engaging with people where they are. Even the SEC gets some value out of promoting their activities, even if it's just awareness of their existence and function and corresponding public support.
That said, now that the Fediverse exists, ideally all of those government agencies would self-host their accounts, either individually or via a server for many different agencies of the same government. It makes sense for the SEC to be @sec@sec.gov or @sec@usa.gov rather than example.com/SECGov . (Which, of course, does not prevent them from having security issues.)
The people who would be responsible for hosting such a Mastodon instance would likely be at least a bit more technically competent than those paid to post on Twitter.
That said, now that the Fediverse exists, ideally all of those government agencies would self-host their accounts, either individually or via a server for many different agencies of the same government. It makes sense for the SEC to be @sec@sec.gov or @sec@usa.gov rather than example.com/SECGov . (Which, of course, does not prevent them from having security issues.)