Because the tooling getting out impacts everyone and thus warrants a public post. Some government information being stolen only impact those customers and only warrants notifying those customers.
Which would be the responsibility of the government customer to disclose to those impacted. FireEye is likely under many contracts that prohibit it from giving out any details on what client data was stolen. Without those details the information is essentially worthless to the public. Who knows if they got the pin number to the VA men's bathroom or all your social security records.
