Good question asked in class today. I do not know.
Media people are hired by folks in Congress and the executive branch to face other media people, but they do not actually hold the office generally. Again, I don't know why.
We discussed this after looking at the graph below on the occupations members of Congress hold. I tried to explain why there are so many lawyers in Congress and mentioned that the principal-agent model of representation suggests that lawyers might be worth "employing" as a representative since lawyers are used to dealing with laws - its what they do. That's not a fully satisfactory answer though.
I do know that lawyers firms and law schools are fertile places places for political activity and recruitment. They are terrific places to tap into political networks that can lead to being recruited to run for office. The same may hold true for business people.
It does occur to me that we probably don't know enough about why certain occupations are over and under represented in Congress. This certainly matters for effective representation - there are 108 business people and 1 union representative in the House. That explains a lot. If anyone reads this that knows of relevant research. let me know what's out there - thanks.