Because VV is completely anti-synergy with how the current iteration of zhongli and his playstyle post beta and post buff.

VV has low base atk yet it’s substat and passive scales off atk. Zhongli himself also has one of the lowest base atk out of all 5 stars which makes it even worse. The 20% shield strength only applies to the user and not party meaning it’s useless for everyone but zhongli on your party. Passive effect requires user to perform multiple NA atk which is a dps loss on a shield support like zhongli because you take away time from your main dps.

The reason why is say this is because zhongli was originally a DPS and not a support in the beta and had higher AA multipliers.