Because you did not diversify strongly enough. Certainly, Google is a great way to get lots of traffic but if 60% of your sales comes from a single source with whom you do not have a signed contract, it is your own fault if you cannot handle your business when the sales tank. It is no different than putting 60% of your investments in a single stock and seeing the company fail, wiping out 60% of your savings. Sure, you didn't cause the company to fail but you did plan very poorly. People keep blaming Google when this happens. But who told you to rely on Google for 60% of your sales, especially when you haven't paid them or signed anything with them with respect to search engine rankings?
Please note that my reply is directed more to the owners of the ecom site than you personally.