> What incentive would they possibly have to not have an export option to let users take their content away?

Wrong question. What incentive would they possibly have to have an export option? If they're going to disappear, what makes you expect that the most likely scenario involves them helping users transition when the vast majority of startups haven't done this?

You can be happy if you get some advance notice that the service is going to shut down. Getting advance notice AND the option to export your data AND that data being in some remotely useful format is hitting the jackpot.