There are many good reasons why bollards are what the Border Patrol wants. Solid walls hide the bad guys from view, and give them a sense of security, as well as lots of time to do deliberate tunneling, breaching, or to stage climbing equipment like ladders. With see through designs, they can't hide from view long enough to tunnel or breach, and those approaching with ladders are seen earlier, to alert responders sooner.
Border security is designed based on the equation of "Border Calculus": Detection Time + Disappearing Time = Time to Intercept. With see through designs, threats are detected much earlier - not when the first head pops over the top. Not only can mast mounted cameras that are securely positioned on the American side stare deep into Mexico, but the new mobile surveillance technology that Officers are starting to get in vehicles will be able to do so as well.
The San Diego Sector started receiving these in December, which allow officers on patrol the magnification to see miles into Mexico for early warning, night vision, and infrared, which can pick out the heat signature of a motionless kid hiding under a bush two miles away.
When Border Patrol has to respond, they know what they will have to face with the see through barrier - is it three women with children, or a dozen narcos with AR-15s? When they do respond, they can issue orders and warnings to those on the other side, photograph them for identification and prosecution (i.e., use their bodycams and dash cams), or pepper spray, tase or shoot them if needed. Bad guys know they may be being observed and filmed at all times.
Bollards can not be rammed by commercial vehicles - they can stop a speeding dump truck. Their reinforced concrete foundations are at least two feet thick and six feet deep, so no hasty tunnels for kids to belly under. Their heavy steel columns are filled with massive concrete and additional rebar. The steel exterior defeats sledgehammer, jackhammer, and hammer and chisel attacks that bare concrete is subject to.
They have been in use in active hot spots on the border for over fifteen years, and have proven very hard to breach. They are basically maintenance free, in contrast to the existing secondary barrier in San Diego, which is breached more than three times per day, on average. In the rare cases where bollards are breached, detection and repair are easier, quicker and cheaper than other designs.
The 18 foot design with anti-climb plate has been proven in practice to quiet busy stretches of border. As tall as the roof of a two storey house, they defeat/deter most men and almost all women and children, even with ladders and ropes. Free climbers (without ladders or special gear) are almost all defeated by the design (when properly installed, without gaps in the plates).
With ladders and ropes, people can climb Mt. Everest, or sheer concrete walls; but beyond just defeating free climbers, bollards bring a lot of powerful operational advantages to Border patrol Officers, over that of opaque solid barriers. Their effectiveness has been well tested and proven in practice.