WebM uses more memory, it is less widely supported, uses more resources when playing, and is currently less efficient compression-wise than WebP.
About FLIF, I was recently checking it and it's indeed a very interesting format. Notably because it can be used on any type of image. I assume it hasn't pickep up steam because it doesn't have the backing of any big sponsor. Google is pushing WebP, and introducing another format at this time is probably not worth it.
FLIF is interesting, yes, but after doing some more research into it I came to the conclusion it doesn't hold any promise as an image format for the web.
The progressive streaming is a cool trick, but if you actually use the progressive stream to embed lossy images in your web page, you end up with lower quality than if you had just used JPEG in the first place, never mind something newer. The difference was pretty stark.
From: https://developers.google.com/speed/webp/faq (Why not simply support WebM in <img>?)
WebM uses more memory, it is less widely supported, uses more resources when playing, and is currently less efficient compression-wise than WebP.
About FLIF, I was recently checking it and it's indeed a very interesting format. Notably because it can be used on any type of image. I assume it hasn't pickep up steam because it doesn't have the backing of any big sponsor. Google is pushing WebP, and introducing another format at this time is probably not worth it.