Technology

It's been a while since I learned this but yeah we were taught it significantly reduces images in size, though in quality too (mostly because of the 256 colors limit, otherwise it is technically lossless IIRC). PNG results in slightly smaller files with much better colors and alpha channels so yeah by comparison gif isn't that good, but to be fair, PNG was created as a direct improvement over gifs for single images compression/encoding, and quite some time later too.

Adding to that, video encoding and compression algorithms have gone so far now that encoding basically any video longer than a few frames as a gif is a waste, but that's because these hardly store any actual still frame IIRC, it's mostly codecs-based wizardry which, for a simple explanation, can cheaply encode several frames by basically saying "this whole area stays the same color for X frames" and even moving blobs of pixels across multiple frames, whereas gifs, by design, store each individual frame making up the video.