JS Bloat
There was one page I accessed recently where I was having issues with the page. I downloaded the page and looked at the source. The payload (data I was interested in on the page and what the page purported to contain) was about 1 Kb. The source for the overall page with all of the scripts (not counting referenced but not in-line "third party" items) was 220 Kb. With bloat like this it is no wonder the pages load slowly.