The reason is dacs change and they get better
But amps not really a good amp ten years ago
Is still a good amp today. But it's not the same with dacs
Another thought is do not get an a DAC with a preamp or vine control
In it or one that can be disabled is fine.
A preamp with an amp is better. Dacs sometimes use
Lesser components in preMps and volume controls
Just some thoughts go separates