The downside here is, should any vulnerability be found in the One True Implementation, every consumer is now vulnerable as well.

Just as you shouldn't let a crop go monoculture, your software should not all be built on one or two pieces of tech.

What happens when dbus is replaced? Now you have to move onto the new, broken thing, and change your code to adapt, giving control to others over your program.

There are valid reasons to not just cargo cult dbus.