...but what? Looking back is a standard technique used before merging into another lane. Also, your contention that Mr. Ratliff was "off to the side from where drivers are more likely to look for traffic" is problematic, since Mr. Ratliff was using the legally designated bike lane, where drivers are held responsible to look for bicycle traffic. The idea that "drivers are more likely to look for [bicycle] traffic" outside the bike lane is not an issue, since the burden of safe entry or crossing of lanes is upon the vehicle operator with entering the street from the driveway. Since a bike lane is a legally designated lane for cyclists, arguing that drivers are more likely to look elsewhere for cyclists does not make sense.

But cycling defensively is always a good idea, and leaving a bike lane that poses any hazard to a cyclist should always be an option.

No, the driver was at fault. Every crash is not the cyclist's fault.