Why do private images load slower than public?

Do private images only load the full size image?

Public image thumbnails load a small image to improve page load speed. They do this through CDN. The URL is something like

https://stringofnumbers.cdn.bubble.io/stringofnumbers/image.png?w=64&h=42&auto=compress&dpr=2&fit=max

The w=64&h=42 part of the URL is what’s critical. Instead of loading 1920x1080 image it’s only a 64x42 image…which is fast.

The same private image thumbnail loads the FULL SIZE image. It download the 1920x1080 image to show a 64x42 image…Why?

Am I wrong here? Is this a bug?

A private image is when you upload and “attach this file to” a thing.
private