Because they aren't stock and take up an entire commander ability slot, unlike the T-70's ability.
Their downside is only becoming active while being stationary, which isn't something you want to do with your tanks in CoH2's highly mobile gameplay. So unlike abilities like the T-70 recon mode, you can only use them defensively. And in order to be powerful (arguably overpowered but that's up for debate) on recon units (222/251) you need to get them to vet 2 and 3 first to get any additional benefits over regular vehicles, so there is a significant investment involved and you need to keep them alive. Without their veterancy sight bonus, spotting scopes offer no special benefits for recon units compared to regular vehicles.
Being stationary is not a downside for OST, not really. 222 can easily be vetted up to 3 in 3v3+. Either by harassing on some wide open maps like steppes or by shooting down planes.
E8 takes up a command slot and is still a useless tank in all but 1v1s (as far as I see, it's great there). Spotting scopes are not really used in 1v1s since being static there is a no-no for any faction. Although can help when expecting an attack. I've often seen vetted 222s parked in safe spots just spotting with 70 range. And chasing it can be disastrous:
a) you're diving a light vehicle with 18/16 target size
b) you're diving against a faction that has stock access to mines, widest arc MG and longest snare (aside from fussies).
Probably the best scout mechanic that was implemented was in Age of Mythology, Atlantis faction those Oracle guys. When they stood still, the vision would be improved in increments. Move and you lose all of it and have to start again. That way you can't just move a bit and stand still again and have 70 vision.
All you said is legit, but stretched. There are plenty of command abilities that take up a slot and are near useless in both axis and allies.
Rifle company new halftrack (don't know why you didn't add the mortar ht but ok)
Cav rifles being 1CP
OST reserve armies, urban pgrens being 2cp (never should have existed and instead should have been some other pgren version)
Soviets with the no-income booby traps, conscript/penal repair tactics, partisans, 45mm at gun
Just to name a few. The RAM + offmap combo has been nerfed although it was doctrinal and the only way soviets can kill something extra heavy, not to mention the 99% chance of losing the T34. Now, soviets can only kill extra heavies in teamgames if they coordinate well AF.
What are you explanations for those?