To be honest, I really don't know. It has been there since the beginning of the game (Pre-Western Front Armies). I never heard people complain about it, but I believe it's supposed to work with defensive strategies like having a machine gun bunker covering the entire 'denial zone' to prevent minesweepers from getting rid of the mines.
Though I guess it's hardly ever used other than that considering that vehicles and tanks can crush it and get away with it.
I think the best way to use them is on the flanks where most players don't pay attention to. Though I can't continue due to the fact that I have very limited use of S-Mines.
I think its just when a unit is useless for a long time, people just accept it and move on. Penals have been garbage for almost as long as Coh2 has been alive, people mention it sometimes but for the most part its accepted because "reasons"