Why don't we hear more from the President's cabinet?

Most of the real work done by the executive branch happens in the agencies with little or no direct involvement from the president. Why don’t we hear more in the media from the department heads directly in charge of what the agencies are doing?

Probably because the vast majority of what they do is really, really boring.

we do hear a lot from Secretaries of State and Defense. Not as much from the others

There is mass media and specialized media. Most of what the Cabinet are doing is not of interest to the general public so are not covered by the mass media. However it is of interest to specialized groups so specialized media cover them. So the agricultural media are covering what Secretary Perdue is doing and the education media cover what Secretary DeVos is doing and the media read by Western ranchers and miners are covering what Secretary Zinke is doing.

I think it’s the West Wing effect. The Presidential staff has grown over the years and a lot of decision making that used to occur in the separate departments is now occurring in the White House.

We do hear from this Cabinet, doing what they were selected to do. (Trump’s own lead-in to this discussion may also amuse.)

If you meant that the Secretary should comment on the doings of his/her own Department, you overlook that many of these appointees have no competence in the Department they were chosen for, and no interest in learning or managing.

I think it depends on the individual cabinet member and administration. I’ve seen the Secretary of Energy on The Daily Show with Jon Stewart during the Obama administration and the Secretary of the Treasury and the Surgeon-General on various shows during multiple administrations. Some of these officials take the public outreach part of their job very seriously.