There's an issue with openly & freely available financial data. It tends to be limited (i.e. you need many sources to answer the questions you want and not just

There's an issue with openly & freely available financial data. It tends to be limited (i.e. you need many sources to answer the questions you want and not just the questions a particular source is able to answer). And if you're bringing in different sources of data, each source requires custom fetching and parsing, along with being just annoyingly slightly different from other sources. Even if the value is given on a per-day basis (which is a huge assumption, lots of things like interest rates are published much slower), you have things like "is the value at the start of day, end of day, market close, median? What time zone? Which exchange? What about days when the exchange was closed? What about odd exchange hours or halts?", "what's the date and time format, what's the naming convention?"