BBM92 and entanglement based QKD relies on quantum entanglement and entanglement photon source (EPS).
Before such sources are easily available, experiments on entanglement needed to be performed, proving its properties and the quantum aspect. Einstein called quantum entanglement a "spooky action at a distance" since 1935, as it was not yet seen working. Trust was missing.
It is from 1982 that quantum entanglement was proved through the work of Aspect, Zeilinger and Clauser, that was later recognised with a Nobel prize in 2022. From then, EPS became a hot topic in labs, leading to new, smaller, and better performing sources like the one from Kwiat in 1999.
Today, they are no longer laboratories only, as they are sturdier and transportable.
It can now be trusted that the EPS works and can be delivered up to you, thanks to a Nobel prize and years of refining the structure.