One good reason would be (as he says) that it is flaky. eg how does it handle newlines, commas, tabs and non-ascii characters in data? I've had to pull dirty data between systems before, and csv as the lowest common denominator tends to be lossy as there's no spec on this stuff. Some systems (eg oracle's csv import) do support forms of escaping, but they're not interoperable.

I see they support other file formats & json here, but a nice to have would be to use the google spreadsheet url: https://developers.google.com/chart/interactive/docs/spreads...

Grabbing data directly from Office365 is also possible: http://cwebbbi.wordpress.com/2012/07/24/consuming-odata-feed...