The thing to understand about making the border harder to cross is that it drives permanent immigration instead of allowing temporary seasonal immigration.

Before they made the border harder to cross, seasonal/migrant workers could go home and come back relatively simply. When they made it harder to go home and come back, the incentive was created for temporary workers to become permanent immigrants, legal or otherwise (but given the drastically underfunded legal immigration system is bottlenecked and legal immigration takes decades, that means farm workers have to come illegally and work under the table and that’s not something the anti-immigrant folks seem to want to end). That there is demand for their work (and basically without them it’s not met) should tell us all that there’s no will to enforce labor law and attempts to control immigration at the border (and not in the labor force) drive illegal immigration