A converter that meets its specification on a test bench may not meet it on a die beside a switching regulator and a digital block clocking at full rate. Supply noise, substrate coupling and thermal gradients all shift analog performance, and none of them appear in a standalone schematic simulation.
Which is why converter IP is as much an integration discipline as a circuit one. Floorplanning, supply partitioning, isolation strategy and post-layout verification across corners determine whether the specification survives the journey onto a real die.
Resolution, sample rate and architecture are selected against the application rather than offered as a fixed part, because a sensor front end and a communications receiver want very different converters.