Cronjob not updating sitemap.xml

[Peter Jonsson]

I did a test increasing cronjob to every 5 min but the sitemap didn't update the listing.xml even if there was a new listings.
Why doesn't the listings.xml get updated on cronrun? Isn't this why we also use sitemaps, to tell google bots that new listings have been added?

What decides when the listings.xml are updated?
Shouldn't that be updated like every time a new listing is added to the site or removed so the spiders know where to look.