Why does Spotify Ad Analytics recommend a javascript pixel instead of an image pixel?

JavaScript pixel implementation is required get the best details to paint the most realistic story of attributed events.  In the event an image pixel or server-side GTM is used instead of a JS pixel, the following limitations apply: 

• No access to Spotify Ad Analytics debugger
• There is no first-party cookie dropped, which limits ability to detect return website visitors (multiple actions from the same user across multiple sessions)
• No landing URL detection
  • For server-side GTM: Can be resolved by sending referrer header