Do people just target lower tiers because..?

This has happened numerous times to me but in this situation it just baffled me

So Im in a VK 30.01P in an uptier and there is a VK 100.01P around the corner

Theres a the derp gun BZ-176 and an autoloading SMV CC-67 infront of me already aiming at the 100.01p around the corner so I roll up to shoot too (I was hoping to track him to make it an easier target for my teammates)

Keep in mind both me and the BZ are at full HP but the CC is at 200 HP

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The VK stops reversing and proceeds to blast me (There is rubble hiding my hull so it's only my turret, the BZ and CC arent hulldown) for 400 instead of shooting the already extremely low CC who is 100x more of a threat than me?

I can't even pen his cupola so I can't do damage to himThe BZ and CC then shoot the VK to half health

Why shoot the tier 6 instead of the really low autoloader who is tier 8, or the derp gun BZ?I know damn well he could've damaged the CC because they weren't hull down, and he could shoot the lower glacis. THE FUCKING BZ WAS SIDEWAYS HIS SIDE WAS FREE TO SHOOT

This has happened multiple times to me where the higher tier I can't even pen shoots me instead of the major threat next to me that can

Can someone explain why??