What was the purpose of using lottery instead of land run

The expression land run refers to a practice used in the US through which previously restricted land was offered in first-arrival basis. Among such events, The Oklahoma Land Rush of 1889 was outstanding.

This system was substituted by a lottery in order to exercise more control over the land distribution proccess. Some participants in previous editions had reported that there were "sooners", people who had arrived to the territory before the legal date and, trying to expel them afterwards was very difficult due to long judiciary processes.

to act quickly in times of danger to the united states

because you have to act quickly if you want to live/survive.