While weight is a factor in professional car racing, and while I've built a go-kart that is significantly lighter in weight than a professional racing car, it is not a particularly impressive achievement that I have managed to do so, and I wouldn't think to criticize a race team for the weight of their vehicle.
Good thing we’re discussing JavaScript library sizes and not cars in random contexts, then.
77kb gzipped is massive considering it’s only doing one thing. If I want my website to load in ~100 milliseconds or less (or even 1 second or less!), I absolutely do need to pay attention to all the libraries I add.
I can and do criticize software developers for making hideously bloated websites because they don’t pay attention to what they add. Not only are a lot of modern websites wasteful, they’re painful or outright useless on slow mobile connections—not a problem for software developers on fibre networks, beefy dev machines, etc.
So it turns out that the use-case for a polyfill of a 77KB image decoder isn't particular suited to a site you want to load in sub 100ms. Oddly, though, that's not the only usecase in the world, and there are circumstances where saving ~30% on every image load turns out to be significantly more efficient than not loading a 77KB JS library.
In other news, I also chose to forgo adding a 15 lb. fuel pump to my go-kart, despite the fact that every NASCAR team in the world uses one, and my go-kart drives just fine. I should go tell the NASCAR teams that fuel pumps are a terrible idea. I clearly know something they don't.
There's a lot of images online that are 1MB. If you're, say, displaying a gallery of photos, you may have saved more in bandwidth using this library plus several smaller images.