Facebook vs. promoting your own website

I have somewhat of an interest in marketing and I find it to be, for lack of a better word, stupid that businesses with their own websites promote their facebook pages instead of their own website. Don't they realize that they are just making more money for facebook and losing money from their own website by doing this? I believe that facebook has really changed things on the internet, for the most part, for the better and I do think that businesses can use it to their advantage, but, some just seem to jump on the bandwagon without really thinking it through. I think the smarter, more profitable way for businesses to use facebook is to post teasers and link to their own websites, instead of just putting it all on facebook. I see this sometimes, but I wouldn't call it commonplace, at least not yet.