It is because they were crude. The further east you go in the US, the cruder. Originally (think pre-US) lot lines had some sort of small boundary marker such as a stream, stone wall, tree, boulder, etc...  These things move and deteriorate over time.  Properties that have structures built on them are a little easier if there is a plot plan that lists the setbacks and frontages.  

Remember most property was divided pre-computers and most people did not know how to determine longitude and latitude so measurements from natural boundaries were typical and subject to change over the centuries.

I'm sure places that have large, observable fault lines have had the types of changes you mention, but here in the east coast land disputes are mostly from inaccurate methods used to describe lots and people sort of guessing where their lot lines are.

If you look at a deed it will typically state that the property is bounded by land of Smith, Jones and O'Brien and which direction and how many feet each lies, not an exact GPS coordinate or even a long/lat.

There are generally accepted real estate definitions and laws to handle erosion and accretion and there generally is no remedy other than the owner either benefits or suffers.  Beach front property owners deal with this the most, although I would imagine fault line properties and properties that contain Volcanoes also would fall under the same practices.

If you are not experiencing accretion or erosion, your 1000 sq ft lot is 1000 sq ft, with its position relative to the neighboring lots.  Because lots may only be off by a few feet or inches here or there, the cost to standardize would not be worth the expense. Most properties that are subject to dispute have some sort of plot plan relative to the structure making it easy to resolve by a survey.