SD is doing it for your protection of course.
If you went and looked at the price on the camel and then decided to click on the amazon link from there then SD wouldn't get it's kickback. It's the same reason they block cashback links. If you get the cashback then SD doesn't.
Is that why? That's silly. I never go through camel--I merely do it to check prices. That is making sense regarding CashBack links--normally I'll click through from SD and then open a CB window (or reverse order)... either way I always get my CB. I figured most sites weren't intelligent enough to limit referrals to just one per transaction--I'm betting SD still gets a cut even with CB active.