vampires feared holy symbols and it seemed quite traditional.
The efficacy of christian holy symbols on vampires usually imply the existance of God and that is not palatable to most modern gamedevs or the megacorps that own them.
It's an interesting worldbuilding conundrum, as vampires are traditionally handicaped by a lot of rules, and these rules are generally enforced by God, protective spirits, what have you. For example, how vampires often need to be invited into private homes (IIRC, something that's true for Vampyr as well).
Unfortunately, a lot of vampire media and their creators don't feel a need to explain any of this or worse, just handwave it.
Trust me, vampires would be super duper interested in why there's an overwhelmingly powerful force stopping them from doing certain things. And they have the egregiously long lifespans and resources to figure it out.