Why most of the gram-negative bacteria are pathogenic?

We hear more about Gram-negative pathogens (E. coli, Salmonella, etc.) because they make good news stories and are generally associated with transmission in improperly handled or prepared food. However, there are many pathogenic Gram positive bacteria as well - Staphlococcus (including MRSA), Streptococcus (such as strep throat), etc. Also, there are many Salmonella species that are non-pathogenic, as well as non-pathogenic E. coli, Enterobacteraceae, etc. So I'm not sure that most Gram negative bacteria are pathogenic.