Loosers study tactics, winners study logistics.
Same reason we don't use walkers and mecha. We got the tech for them, but one guy with an old timey grenade put in a sock then dipped in axel grease thrown onto a knee joint means you've lost a unit. One that's really high tech, expensive. and finicky. Also the crew's probably dead, so you gotta find more men and train them for that as well.
In the case of landships these behemoths could only run on flat terrain such as central africa, the steppes of asia, or the great plains of north america. They'd also be followed by an entire convoy to meet their fuel and matiance requirements. Regardless of what they're burning.
Similarly while the sherman's not a death trap the fact that it's built so the crew would survive and the parts are easily replicable means if hanz disables one unless he tripple taps it and hunts down the fleeing crew. Some engineering truck from behind the lines is going to come in, drag that fucker back to the depot weld it, replace it's parts, and it'll be back on the road in a few days.
You hit most panzers? Even without penetrating it you'll knock out bolts, gears, and electronics. Which means they have limp home order new parts from the factory in Kurglepltaz, then wait on delivery. This is compounded by every other unit screaming at them for parts, and the high command screaming at them to pump out more tanks and stop wasting time making spare parts.
This is assuming hanz, and his tank survived the encounter, and Kurgleplatz isn't staffed by slaves.
Fantasy lets us ignore logistics and go for pure rule of cool.
It just also happens that fascism, and authoritarianism more generally run on that same fantasy/myth logic.
Because anyone who tries to say to the regime's leader or his underlings "I'm sorry sir we can't do that." is gunna get shot and/or thrown out the window along with his expense reports.
For more modern examples, look to how china and russia operate.