Here's what they wrote:
Thank you for your interest in Google AdSense. Unfortunately, after
reviewing your application, we're unable to accept you into Google
AdSense at this time.
We did not approve your application for the reasons listed below.
- Adult content
Adult content: Currently, only Google ads that we classify as
family-safe are available through the AdSense program. We've found your
site to be predominantly adult or mature in nature. Therefore, we're
unable to display relevant ads on your site. Please review our policies
/policies?hl=en_US) for a complete list
of site content not allowed on web pages.