The others can and will shift, amplifying the waves or undergoing liquefaction. None of which you want to experience beneath your home or building.
When bedrock is unavailable, a large area of loose soil is dug out, we do some lab tests on it, and we can determine the maximum compaction at which we can put it back. This is very effective, and just about every modern house sits in this "fill" so one extent or another, as sometimes our artificial compaction is actually better that what Mother Nature did.
when the earthquake is happening, and your house is built on loose soil, the soil will shake around and move to one side and then your house will sink into the side the soil has shifted opposite of.