You'd think so but when the use case involves dynamically retrieving fresh data it becomes one of the last things to work on. Lots of people have CSV data and it makes sense to support it but since it's generally a manual process it doesn't deliver a good "flow" for the customer. If they have to repeatedly export/import their data manually to have the chart data update it'll seem like a chore.

Compare this to connecting to a customer's database directly. You can refresh your (cached) chart data on your own schedule and the customer doesn't need to be involved at all.

Oh and if anyone is thinking, "Yeah but I can schedule a cron job to extract the CSV file and publish it every X minutes", yes you could do that but again that's work for the customer. If the pitch is "sign up, plug in to your database, and boom charts!" there really should be a "schedule automated cron job" component.

All that aside, it is useful to be able to manually add data like this. Particularly for static data where the manual work is infrequent.