I used to be one of those people. It just made sense to me when I was (I still am to some extent) more naïve than I am today. But then I also used to think "it makes sense for everyone to eat together at a community kitchen of some sort instead of cooking at home because it saves everyone time and money" but that's another tangent for another day. The reason I bring it up is I used to think if it is shared functionality and it is a small enough domain, there is no need for everyone to spend time to implement the same idea a hundred times. It will save time and effort if we pool it together into one repository of a small library.
Except reality is never that simple. Just like that community kitchen, if everyone decided to eat the same nutritious meal together, we would definitely save time and money but people don't like living in what is basically an open air prison.