It's a religious thing in general.
In my country there's examples of religious sites changing hands several times.
For instance the San Vicente Mártir Church, were transformed into Cordoba Mosque when the Muslims invaded the Iberian peninsula, and then after the Reconquista Christians turned it into a Cathedral.
Religion is about power. And you cannot let the old power to preserve their place if you want your new power to hold control.
It's not about being vulnerable. It's probably a very tight software.
It's just that Meta stores the private keys of the e2e encryption. So they can decrypt any and all chats if they want to.