This is incredibly detailed; in short, CDNs, cookies/authentication , tons of subdomains, and 3rd-party/user-generated content make it a pain to move onto HTTPS.

I was chatting with a non-engineer friend about why it's hard to estimate how long tasks often take, and this seems like a prime illustration: the dependencies are endless.

I also love the Easter egg:

"The password to our data center is pickles. I didn’t think anyone would read this far and it seemed like a good place to store it."