Because you should be downvoted for this.
People who have long-standing health conditions, that they have perhaps battled their whole lives, don't need people on the Internet arm-chair quarterbacking their treatment. They have medical professionals that they've worked with for years and trust, they have almost certainly done more research than you or I about their condition, and they have heard the latest fad cure-all from everyone, everyday, for years. They get it on their facebook wall, they get it from well-meaning (but poorly informed) friends and family, and they get it from strangers on the Internet.
Don't be that stranger on the Internet. Your intentions are positive and laudable, your actions are not.
In short: Unless someone has asked for advice about treatment options for their chronic condition, it is probably impolite to offer it.
Source: Conversations with friends with MS, CP, disabilities, autism spectrum disorders, and various trainings in how to provide safer spaces for people with a variety of conditions.