Ever try walking a mile with a 36-foot aluminum ladder that weighs 80 lbs? It's not easy to walk with (or hide) a 36' ladder. A 25-foot wall needs a 36' ladder at 75° for a safe working height of 25.5 ft.
Moreover, the Border Patrol could easily throw a grappling hook over the wall and pull the ladder sideways and then use a 2nd grappling hook to grab the bottom of ladder and pull the ladder over the wall to confiscate a $420 ladder.
Lastly, a bigger ladder is far more easily detected, even if strapped to the top of pickup truck.
A Tunnel Dig can be detected by backtracking sightings and routes of illegals as tunnels are not easily moveable and concentrate the path to entry.
Also, a lot of time is needed to dig a tunnel, hence, there is increased illegal activity on other side of border that can give away the location of the tunnel entrance.