SDN has a lot of traffic but look at it this way. There are a number of conflicting interests here. It isn't all physicians and med students -- there are a lot of other healthcare related paths represented on here. It isn't all allopathic. It isn't even all folks who will ever apply to or get into a US med school. There are folks from other countries on here. There are folks who are attending offshore schools. There are lots of people on here who don't get to vote in US elections. In truth, the number of folks who regularly use SDN and have a vested interest and a say in the issues you mention is quite small. You probably could start a bigger organization at whatever school you attend. Or, as folks have mentioned, you can join the AMA or another organization which already has a decent sized membership.
But bear in mind that being a big group doesn't give you any clout. You have to hold some of the cards. Premeds hold none. Med students hold almost none. Residents hold a few, but largely insignificant, cards. The folks who have the power to change things, if they organized and lobbied simply don't have a lot of the same interests that folks on here have.
As for the issues you mentioned, bear in mind that physicians are horribly organized and lobby poorly. Their opponents (eg in reimbursements the insurance lobby, or in terms of malpractice both the trial lawyers and insurance lobbies) are amazingly well organized, highly funded and lobby well. Folks in medicine aren't pulling in a unified direction, and aren't willing to contribute funds toward lobbying for the kinds of things you mentioned. And medicine has a big image problem -- the public perception is that doctors earn too much -- so you get no groundswell support when you push for things like better reimbursement terms or medmal protection. The public things doctors are magic and that bad things only happen with negligence. So protecting doctors interests has not touched the hearts of americans even though the current president tried hard to float plans to allow obstetricians to "share their love" with their patients without fear of being sued.
