This seem the case because irl the tank usually got hit in the turret not to mention unprotected ammo that are prone to catching fire even with a little spall .
But if ammo in the carousel or anywhere else got a direct hit that would be a different story. (like op mention)
To OP i want to mention that
gasoline tank can explode but it’s rare ( if there’s a specific fuel-air mixture [fume concentration] within )
self-sealing fuel tank would be enough to prevent that. Unless the fuel tank are rupture which will spread the fuel everywhere. Then there are automatic fire suppression system to help with that.
diesel tank cannot explode ( It can be made to explode but only if you spray it in fine mist and then apply large amounts of pressure or temperature to it) but due to diesel evaporates less quickly. If fuel tank are rupture which would lead to the tanks compartment being covered in diesel oil. that may or may not catch fire. Then again there are automatic fire suppression system around.
So fuel tank explode rn are a bit silly given how Gaijin did nerf ammo catch fire / burning change.