It is the site, not the network speed. I have a fast connection, and most other sites are much faster. Slowness is most irritating when paging through multiple photos in a post.
Presumably it is an issue around compute, storage or network issues within the site/hosting environment itself. While I understand this is an economic tradeoff for the owners, it would be nice to at least see this site to be average in its performance, and it is clearly not. This sort of thing creates a friction that, with a good alternative, will drive users away. I am sure the site management knows that and is making a calculation on what we will tolerate.
Dave