I don't know either, but my suspicion would be that they simply haven't kept up. Not that tags are hard to do:
use AppleScript version "2.3.1"
use scripting additions
use framework "Foundation"
on returnTagsFor:posixPath -- get the tags
set aURL to current application's |NSURL|'s fileURLWithPath:posixPath -- make URL
set {theResult, theTags} to aURL's getResourceValue:(reference) forKey:(current application's NSURLTagNamesKey) |error|:(missing value)
if theTags = missing value then return {} -- because when there are none, it returns missing value
return theTags as list
end returnTagsFor:
on setTags:tagList forPath:posixPath -- set the tags, replacing any existing
set aURL to current application's |NSURL|'s fileURLWithPath:posixPath -- make URL
aURL's setResourceValue:tagList forKey:(current application's NSURLTagNamesKey) |error|:(missing value)
end setTags:forPath:
on addTags:tagList forPath:posixPath -- add to existing tags
set aURL to current application's |NSURL|'s fileURLWithPath:posixPath -- make URL
-- get existing tags
set {theResult, theTags} to aURL's getResourceValue:(reference) forKey:(current application's NSURLTagNamesKey) |error|:(missing value)
if theTags ≠ missing value then -- add new tags
set tagList to (theTags as list) & tagList
set tagList to (current application's NSOrderedSet's orderedSetWithArray:tagList)'s allObjects() -- delete any duplicates
end if
aURL's setResourceValue:tagList forKey:(current application's NSURLTagNamesKey) |error|:(missing value)
end addTags:forPath: