Blog images are not optimized for mobile

Hi! When a customer views our blogs on mobile the lead image is not optimized for mobile. The image displays correctly when you view the category page https://www.realnoni.com/Blog/ however when you click on a specific blog the image then completely distorts https://www.realnoni.com/Noni-Ice-Cube-Recipe/

how do we fix this?

category view

blog image display correct.PNG (202.71 KiB) Viewed 1500 times

individual blog view

blog image display.PNG (211.03 KiB) Viewed 1500 times

When editing your blog, you can click on the image then check the box that says "Responsive"

Is there a reason that the system does not automatically default to have all images format for mobile responsive display? What is the benefit to not optimize for mobile?