Hello,
Thank you for the excellent question. The Westview theme was designed only to use the background on Pages, not posts and archives.
In order to override this and show your background everywhere, navigate to Customize -> Advanced -> Custom JS & CSS and copy-and-paste this CSS rule into your Custom Theme CSS box:
.palette-primary.archive .site-content, .palette-primary.archive .site-header, .palette-primary.single .site-content, .palette-primary.single .site-header, .palette-primary.blog .site-content, .palette-primary.blog .site-header {
background: unset;
}
I hope this helps