One Offs. A lot of research results in one-off code. You may not go back to this dataset, these ideas again. When you do, sometimes years, later, you go, oh shit, this is hard to work with. So then you begin to build better structures, do the extra work it takes to make things easy to apply to new purposes or to accept new (but slightly different) datasets. It takes time and effort, and money. And that is where it all breaks down. Most scientists have to be jacks of many trades to get by.