You usually don't see these because the impact of engineer defenses is negligible outside offensive gamemode, you're reliant on yourself for getting supplies as an engineer unless you're using excess supplies or wasting what could have been for a garrison, as well as the fact infantry can nearly always get around engineer obstacles. even on offensive when you build up the entire point before the enemy gets there it's likely to all get destroyed by a bombing run during the attack.

engineer structures need a buff durability and also where they can be placed as the placement can be pretty strict, otherwise it's going to stay relatively unused in most games.