It's likely a combination of things.

Firstly, most people don't know what the difference is between a low quality image with compression artifacts and a nice clean, quality image.

Also, many people don't keep their screens clean, or they could be broken. So many times my friends or family will share a photo they took with their phone and it's blurry as hell because the glass over the lens is dirty and smudged.

Lastly, it could just be how you view the image. You could be viewing a smaller or more compressed version because your app is trying to save space. Or it could be that your screen itself is low quality.

But even though the difference in quality is lost on some people, that does not mean all people. I think it's important to provide higher quality content because it shows respect to the creators of the content as well as the people you share it with. Not only that, but if Lemmy is the place to find the higher quality content then that sets it apart from all the other social media platforms.

Here's a comparison:

I used https://www.diffchecker.com/image-compare/ - I uploaded the two files there.