Why are some earthquakes more disastrous than others?

As an example we can look at the 2010 Haitian earthquake and the Japanese Tohoku earthquake from 2011. The Japanese earthquake resulted in a much higher Richter scale reading compared to the Haitian earthquake, however, it had fewer casualties. This was partly due to good disaster-management and earthquake-resistant infrastructure. Furthermore, Japan being a HIC (high income country) meant they were able to manage and distribute medical care, food, shelter, etc and organize rescue efforts very soon after the disaster.

Haiti is a LIC (Low income country), this meant they were unable to provide survivors with adequate or timely assistance, and rescue efforts, post-disaster management or relief were also lacking and were heavily sourced from charitable countries and organisations which of course, took time to organize. This along with vulnerable infrastructure caused casualties in Haiti to be magnitudes higher than in Japan (something on the order of 300k vs 15k).

Whilst the two earthquakes aren't exactly similar, this should shed some light on the importance of disaster mitigation and management strategies on a national scale. In addition to the above, it is important to realise that while the Richter scale (or whatever scale used) does provide a magnitude for the strength of the earthquake, how this translates into human casualties and destruction of property also depends on factors such as the quake's proximity to faults, the depth of quake, density of the local populations, presence and quality of earthquake resistant structures, the efficiency of rescue operations and disaster relief, infrastructure in place to deal with evacuations, rescues, medical aid, etc.