Earlier quoted context omitted.
Yet for the same compatibility reasons most people stuck with .jpg and .htm, at least in the Windows world. Even now it's very unusual to see a .jpeg extension on a filename. The metadata that Macs kept in the resource fork go way beyond file type and creator too. It included things like the file's Icon, creation/modification information (so it would survive a trip over the Internet!), loads of stuff for applications…
You don't see .jpeg because people are used to .jpg. There's nothing incompatible with long names that we care about. Also, that Windows feature you mention is called ADS - alternate data stream.
.jpeg.photoshop.ro.creat127339292....
The filename extension is the bare minimum of metadata for a file and not easy to extend.
Even then Unix systems will skip even that minimal metadata and force you to messily search for magic numbers at the start of the file and make a guess.