I can see why the manufacturer would want this. As a user though why would you? If the rest of the body is familiar and works well, why toss it?

Maybe the sentiment springs from the general culture of consumerism and new-is-better thinking, and historically that's been warranted in the consumer electronics space. Most things aren't really like that though. Humans have long built tools, clothing, furniture, and infrastructure designed to last a long time. You commit resources up front to make sure the thing is of high quality and then benefit for anywhere between decades to centuries. Replacement carries the risk of downgrading. Again, rapid technological advancement has blown this way of doing things away, but at some point parts of the tech plateau and this will need to be rediscovered. For things like keyboards, trackpads, and laptop cases, I don't see how "new" will beat "good" from this point on. Even displays are starting to reach limits. This seems like the right time to be working on "here is your reliable human interface device, drop in whatever crazy magic chip fabs have cooked up every X years to keep it capable."

From a humanist perspective there's another reason to move this way. People like to grow attached to objects and tools. Something has been lost in the shuffle of swapping out our most personal objects every few years.