Borders walls are only as good as the people who staff them. In the following story, it is unclear exactly why the gates were open on the Guatemala side of the Guatemala/Mexico border.

Migrant caravan freely crosses Mexican border after gates were left open, authorities avoided 'confrontation'

Around 1,000 Central American migrants marched freely through the Guatemala-Mexico border on Friday after the gates were left wide open, with Mexican authorities standing down from confronting the caravan.

Fox News

However, not to hard to see given the vast expanse of the border and existing examples of corruption and the money involved that those sparsely populated stretches of border might provide new corruption opportunities.

The Enemy Within: Bribes Bore a Hole in the U.S. Border (Published 2016)

Over the last decade, nearly 200 Homeland Security workers accepted bribes to let immigrants and drugs into the country, a New York Times review found.

www.nytimes.com