wehr is primarily a defensive faction until they reach t3 for their tanks. attacking wehr is pretty punishing if the push doesn't go that well for most allied factions. As soviets, mines act as a defense mechanism that help slow down the wehr defensive creep on your cutoff or fuel if a push does not go as well as hoped and you have a mass retreat on your hands.
pios have great sight range and come with a minesweeper upgrade. why wouldn't you sweep enemy territory. it's just common sense.
The choice is really simple. you either eat a mine with manpower or you eat it with a one-off munition investment.
The problem is that it drags the game down enormously when the risk of getting squadwiped by a cheap spammable mine is so high. Ostheer is forced into blobberino tactics as getting 2 early sweepers is suicide as you'll simply get rekt by allied light vehicles rushes and just having 1 sweeper is not enough to cover anything more than the blob.
Ostheer is the only one that suffers from this problem.
OKW can get 2 sweepers and still have combat effective infantry because they can toggle off the sweepers.
USF can get 2 sweepers quite easily because RE troops can still be upgraded with other weapons to give them a role on the battlefield.
Brits engineers can be upgraded to 5 man squads and extra weapons to remain strong troops even when upgraded with sweepers.
Soviets don't need more than 1 sweeper because the risk of squadwipes with 6 man squads is very low.
Ostheer is screwed. Their squads are the easiest off all factions to wipe with random mines, their pioneers have 0 combat effectiveness when armed with a minesweeper and they have no way of making them any more effective. They are forced to blob or take a huge risk of losing expensive squads to RNG mines. If they do go for more sweepers early on, they lack the troops to perform offensive maneuvers and will struggle enormously against allied light vehicle rushes.