This is a pretty huge topic, but I can summarize a couple major factors.
More population, more damage, more awareness
The effect of a disaster that kills thousands of people and causes property damage in the billions of dollars (current equivalent) is felt much more intensely than that of a disaster of similar magnitude that affects a much smaller population. Note that the magnitudes indicated on these articles are not the same measurements; 6.9 ML is actually bit more than 6.9 MW.
The twentieth century saw huge growth in world population and, more importantly, in population density in and around urban areas. Earthquakes are localized natural disasters that will affect as many people and structures as exist wherever they happen to occur. The 1906 quake in San Francisco, and other large quakes throughout the 20th century, had huge impacts on the world's awareness of earthquake danger, both because they affected more and more people and because modern communication technology allowed their effects to be recorded and broadcast to an unprecedented degree.
(To go way back, consider that when the entire city of Pompeii was buried by the eruption of Mount Vesuvius, "only" about ten thousand people were killed. Pompeii was not a very large city for that time but a very large city still would have had less than a million people living in it, whereas modern urban areas have populations in the tens of millions.)
Seismology is a young field
The basic field of science that underlies seismic design and engineering is only about 150 years old; see A Brief History of Seismology (USGS) for an overview.
Now, it's possible to make a building strong without understanding the underlying science. You don't have to know what makes a building fall down to recognize that when a quake hits, more buildings of one type fall down than of another type. What you can't really do is agree upon and implement the type of evidence-based standards that really impact seismic safety on a broad scale. Architects want to do what looks good, governments want to do what's cheap, project managers want to do what's easy, etc.
First, we had to understand a bit of what was going on; then, when we figured out what we needed to measure, we had to collect data. Earthquakes are not exactly easy to simulate when you're still trying to work out the basic theory involved. So it took some time, just as with aviation technology, before we knew what to do to have the best impact.
Has technology changed much in the past few decades?
Maybe not the technology itself so much as our understanding of the technology. The 1994 Northridge quake is an example of what I mean; we've used a lot of different methods and technologies for a long time without having the empirical evidence required to understand which of them work better than others, or why. There's nothing particularly difficult or high-tech about bracing cripple walls, bolting structures to their foundations or adding reinforcing elements to concrete, once you figure out just how much of a difference it makes (and where it's most needed).