i noticed this in the nether when looking for quartz it isnt that hard to hit a boarder but there are reasons for having it this way eg it greatly reduces the amount of chunks that have to be loaded and saved lets say them move the boarder 1 chunk i think 16 blocks then u have to load up all the chunks in that row and thats a lot of chunks but i think the main reason is that u have to have it somewhere why not there.