Sucker Punch works differently from the other two. This is working as intended.
You can throw a saboteur shock mine anywhere, and you can do the bruiser rush anywhere, because in both cases it brings up a little aiming bit. Indeed, you can even aim a shock mine at a spot that doesn't currently have a visible enemy in it (e.g., to lure a hidden enemy around into a trap), and likewise for the bruiser's rush not targeting any visible enemies.
On the other hand, sucker punch needs to target a specific enemy at close range. To use it, you'll want to ungroup your folks and select a sneak (or have a team of all sneaks also works), so that the enemy's awareness bubble no longer extends behind them. Then walk up behind an enemy during real time mode, and you should see a "sucker punch" icon show up on the enemy to be targeted. The icon at the bottom of the screen is mostly just there to help you keep track of how many sucker punches you have left.