Crossing the border by foot

Authorities have dismantled a major cell of a human smuggling ring that may be responsible for the transportation of thousands of illegal immigrants from the U.S.-Mexico border to Phoenix and other parts of the country, investigators said Wednesday.

Nine people were arrested Wednesday after a yearlong investigation. They have not yet been charged but are accused of picking up illegal immigrants after they crossed the border by foot, and taking them to what are known as drop houses in Phoenix before they were distributed to other parts of the country.

http://news.yahoo.com/s/ap/20101111/ap_on_re_us/us_smuggling_ring_bust

This "human smuggling ring" picked up "thousands of illegal immigrants" "after they crossed the border by foot". In other words, it was a transportation service for people who had already entered the country illegally.

Why are "thousands of illegal immigrants" still "crossing the border by foot"? Both Bush and Obama promised to stop that.