Perhaps is doing some heavy lifting here. I take it from the fact that the lectures are on Functional Programming that OP might not be a front-end developer and might not have the level of care needed for front end to compress the images in a way that renders nicely. So,

Perhaps you ought not judge someone releasing their free teaching materials for a backend class on their front end development, when the site is a centered <div> with purely static elements.

Perhaps you ought to slow down and do some critical thinking before being critical of others.