When a CEO takes full responsibility for these things it doesn't mean that they submit themselves to the punishment that internet users might want. It's the CEO telling their impacted employees that, no matter how well you did as an employee, you would still have been impacted. It's the CEO showing you empathy for the hurt they cause you for having failed to steer the company in a viable direction.

These messages are obviously never going to be well received, but at least people can find comfort in the fact that it's because Dropbox is shifting direction and strategy and not because they were bad employees. Stuff like this happens in business. Maybe you've focused on private sales and want to shift to enterprise sales or fund investments at which point your company no longer needs it's sales and marketing departments because the company mission will be radically different. Changing course is a CEO taking responsibility for the company.

It is what it is.