That's just because they are a handful of people. If there were more, many more, they would be the reason for some urgent action on the part of Gov't to crack down on this kind of immigration.
They had 1000-1500 signed up. This was for the entire month of April. It is a good bet that many did not show up or sign up due to the negative publicity that began before April 1. With President Bush referring to them as vigilantes prior to the start of the project, what should we expect?