Because BtN cites their sources, and most names list an etymology (or historical usage) instead of concocting half-baked "meanings". Look at today's name of the day,
Donald: "from the Gaelic name
Domhnall which means "ruler of the world", composed of the old Celtic elements dumno "world" and val "rule". Also, there's a source page on here that cites the sources for names.
The only "inaccuracies" I've seen on BtN have to do with usage. I remember Pie said that a few of Welsh names on here aren't actually used
as names in Wales (even if the meaning is correct).
BtN isn't perfect but it's definitely a cut above the majority of other sites and supermarket books out there.