It was a combination of the value to others we could liberate by doing that, and the value it would bring to us. As Grist took shape, it felt like a nice self-contained tool (and format) that could be useful at many points in a data pipeline, given its editing, visualization, and summarization functions. And spreadsheets have a long tail of features users want, so it makes sense to open it up to collaborative development, especially given how tech-savvy our users can be.