Why Must Read 10 Actual, Official LSAT PrepTests?

So the LSAT has four non-writing sections with one of them being a reading section. In 2007 the test switched the format of the reading sections so that groups of questions pertained to two passages that related to one another, specifically in how they did and didn't correlate with each other. Prior to that it was just one passage per set of questions. These tests, however, come from LSATs administered in the 1990s. And I must say, that the difference between the example of the 2 passage reading section and single passage section was quite dramatic.