Except actually NTFS does have "extended attributes" in the HPFS sense, which were added to support the OS/2 subsystem in Windows NT. And went on to be used by other stuff as well, including the POSIX subsystem (and its successors Interix/SFU/SUA) and more recently WSL (at least WSL1, not sure about WSL2), for storage of POSIX file metadata.

In NTFS, the streams of a regular file are actually attributes of `$DATA` type; the primary stream is an unnamed `$DATA` type attribute, and any alternate data stream (ADS) is a named `$DATA` type attribute. By contrast, extended attributes are not stored in `$DATA` type attributes, they are stored in the file's `$EA` and `$EA_INFORMATION` attributes. I believe `$EA` contains the actual extended attribute data, whereas `$EA_INFORMATION` is an index to speed up access.

Alternate data streams are accessed using ordinary file APIs, suffixing the file name with `:` then the stream name. Actually, in its fullest form, an NTFS file or directory name includes the attribute type, so the primary stream of a file `foo.txt` is called `foo.txt::$DATA` and an ADS named bar's full name is `foo.txt:bar:$DATA`. For a directory, the default stream is called `$I30` and its type is `$INDEX_ALLOCATION`, so the full name of `C:\Users` is actually `C:\Users:$I30:$INDEX_ALLOCATION`. You will note in `CMD.EXE`, `dir C:\Users:$I30:$INDEX_ALLOCATION` actually works, and returns identical results to `C:\Users`, while other suffixes (e.g. `:$I31` or `:$I30:$DATA`) give you an error instead. Windows will let you created named `:$DATA` streams on a directory, but not a named one.

By contrast, extended attributes are accessed using dedicated Windows NT APIs, namely `NtQueryEaFile` and `NtSetEaFile`.

I'm not sure why Windows POSIX went with EAs instead of ADS; I speculate it is because if you only have a small quantity of data to store, but want to store it on a huge number of files and directories, EAs end up being faster and using less storage than ADS do.