Hi there, welcome to WordPress Trac! Thanks for the ticket.
Just noting that WordPress does in fact have built-in image compression for intermediate image sizes, see the WP_Image_Editor::set_quality() method and these posts for more details:
Increased image compression for custom sizes
WordPress 4.5 increases the amount of compression applied to intermediate sizes by changing the default quality in WP_Image_Editor from 90 to 82. As noted in the proposal for this change, this results in a noticeable reduction in file sizes with little change in visual quality. Developers can override the default image quality value using the wp_editor_set_quality filter.
That said, WordPress always stores the original uploaded image without any modifications so it could be reused in the future to create new intermediate copies if there are any changes to custom image sizes. Since I don't think we want to change that at this time (creating resized copies from other copies would result in quality loss, as noted in #19679), I'm not sure how actionable this ticket would be.
Ticket #37840 suggests adding a new image size to WordPress that is an optimized version of the original image, and using that on the front end instead of the original uploaded image. This appears to be similar to what is being proposed here, so I think the discussion can continue there.
In the future, this could be improved further with dynamic image resizing, see tickets #15311 and #21810.