You may not want to look at XML without a tool, but you could. Or, most likely, you could build a tool to look at the XML. This is a crucial design consideration of XML - even if all XML tooling, open or not, is lost forever, you can still read the XML. Not so with SQLite.
Especially for a document format, this point seems important. That said, OpenDocument is zipped, which, while a simpler and even more ubiquitous format, is still a binary format that requires a library to read, so that detracts somewhat from the point. It's difficult to imagine a future where zip libraries survive but SQLite libraries don't.