While there are sometimes other options, in many cases all of the options are equally bad (or at least deficient in similar ways). There can be many reasons for this, high costs of maintaining a large popular website (like flickr), etc.

What is significant though, is that online there are lower barriers-to-entry than in the old brick and mortar mode, which means that even if there is no other option at present, sufficient dissatisfaction will cause some group of developers to provide one if they see a need. In other words, just because you don’t see a competitor to your service at present, does not mean that one won’t appear overnight. The upshot of this is the omnipresence of a “virtual competitor.”

The lesson: don’t compel your users to create a better alternative.