Perhaps the thing that makes it hated is also what makes it durable.
It's possible to configure in infinite ways.
Any employee can tweak it, adding little workflow features to the shared instance.
These features are often only "designed" in that local context, but clutter up the shared instance for everyone.
So a bunch of ill-considered modifications accumulate.
It's easier to add them than to remove them.
There's no one owner of the whole thing, so it just grows in complexity without bound.
If it were customer-facing, the quagmire would be an existential embarrassment, people would be assigned to clean it up.
But when it's internal, it's easier to just trudge through.
At every step, it's easier to add just one more hack on the pile than to stop the world and try to rationalize it.
It's never urgent to plant a tree.