Yes, Saturday is Homecoming and hotel rooms will be very difficult to get for eighty teams for (think needing rooms for 600 people in addition to an already sold-out Madison area). In addition, getting rooms for an event that was not planned long in advance and for teams that usually cannot commit that long in advance. The mid-afternoon timing allows many teams to return Friday afternoon/evening. In a few cases (Indiana) teams are going to both PreNats, which is on Sunday, and Wisconsin. [Plus women's hockey hosts biggest rival and #3-ranked Minnesota Friday evening => Friday night hotels and volleyball against #5 Nebraska and then Minnesota]
The switch in the timing arose somewhat suddenly as Nationals were going to be in Oregon and then had to be abruptly switched to Indiana State, who also had homecoming that weekend, I think, and would not be able to host PreNats on Saturday, so they switched to Sunday. Sunday does not work for a lot of teams, plus people have run on the course so many times that they do not really need to see it again. In addition, mid-October in Terre Haute and running in warm temps is not necessarily a good test compared to the cool temps expected at Regionals/ Nationals. In addition, the course can have a very hard surface on a dried out course because it is located on top of a clay cap and if it rains, the surface gets problematic. Thus, Wisconsin decided to jump up their schedule to a timeframe that is a bit better for the team in terms of timing for the season (plus they could go to Dellinger, which was moved to the beginning of October).
However, I know what you mean, I have been trying to get people from work to come to the meet and it does not work that well for most of them.