Probably cause if they did advertise on TV there would be a hugh out cry from the LEFT to pass a law prohibiting it ----ie shut them up.
No, no matter how much you want to believe its an anti-gun conspiracy that is just not the case.
The entire US Firearms industry is about 1/6th the size of McDonalds (about $2 Billion/yr whereas McDonalds is about $12 Billion/yr.) National advertising on TV and in large circulation magazines (like Time, Newsweek, Better Homes & Gardens, etc) is REAL DAMN EXPENSIVE.
A small ad in Time Magazine can run you more than $100,000! That's for 1 week of advertising. If you wanted to keep that ad running for a year, that would be $5.2 Million (assuming they don't have some sort of bulk rate).
Thats just magazine advertising (which is a bargain compared to national TV advertising).
When you compare that to
rates for American Handgunner, you'll see that running a full page, full color ad is only $6,595, and that goes to a targeted market (gun owners) and runs for two months.
The best way for gun manufacturers to advertise nationaly (or globaly) aside from advertising in industry specific publications is via
product placement. HK pioneered it and Magnum Research is still in business because of it, but if a gun manufacturer can get their guns placed prominantly in movies and TV shows, that will make them TONS more in return.