One of those reasons is the cost compared to high tech options.
High tech options do not stop border crossing. They only alert you to them. On top of that the cost would likely surpass a wall in the long run. You have initial investment, maintenance, new manpower to operate it as well as agents to actually act upon its data, replacement or updating costs when the inevitable jammers are created.
A wall by comparison has very little of those costs.
Another reason is the ineffectiveness of a physical wal
That is just an ignorant statement that deserves no further discussion.
Democrats know that all a foreign national has to do is get across the border. Even if they are caught, they are just released. A border wall prevents foreign nationals from stepping foot in America and that's why Democrats are dead set against it.
Democrats illegal immigration platform...
Sneak into America
Obtain services like healthcare and welfare paid for by Americans
Vote for anti American globalist Democrats who aid and abet illegal immigrants
Victimize Americans
Get deported from America
REPEAT...
a wall also stops the last step. The reason Obama deported so many people was because he was deporting the same people over and over again.