Why should social media be just one part of a broader content marketing strategy? Because you don’t own it.
You might fall in love with granite counter tops and an all-marble steam shower, but if you live in a rental, does it make sense to invest that kind of money in a home the landlord can throw you out of when your lease is up?
Sure, it makes sense to make the place “yours” but you’re not going to get your money back on improvements to a rental the way you should for an upgraded kitchen or bath in a home you own.
Similarly it makes sense to make your Facebook presence “yours” and to invest time and money there. But it shouldn’t be the only place you’re investing. You should also be investing in properties you own – your website, your blog, and properties under your control.