Essentially, @mac.com is legacy users and was in place from the debut of osX to late 2000s. It required a annual paid subscription to have an email address, lol. Then the short-lived mobileMe era happened, which lasted only a couple years before Apple retracted and replaced it with iCloud, a much more sweeping service. MobileMe was also a paid subscription and included primordial versions of photo sharing and web hosting, etc. The iCloud era starting in 2012 finally ushered in free email addresses and free operating system updates. That's when the business model of large tech companies turned more into user accumulation wars to see who can attract the most subscribers and retain them in their ecosystem of products.

Why are there so many programming languages and frameworks? Everyone has their own opinion on how something should be done. Some of these systems, like AOL, Yahoo, etc... have been around for a decade, and probably not updated much.

Simple fact is that HTML support is different in them because mail clients are so old, or others are allowed to operate in browsers where not all CSS or even HTML can be applied in a secure manner. Older clients have outdated browsers that you'll likely NEVER see brought up to standards; what with Opera's standalone aging like milk, and thunderbird lagging behind the firefox on which it's even built. Don't even get me STARTED on older clients like Eudora or Outlook.