Because your regex is anchored to the start and end of the string, so it'll only find a tag that's on a line by itself:

if (/^\{(.*)\}$/) {
  $tag = $1;
  print "The tag is $tag\n";
}
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Your {TTL} and {LINE} tags are in the middle of the line, so they won't get picked up by the regex.

You could try something like this instead:

while (/\{(.*?)\}/g) {
  $tag = $1;
  print "The tag is $tag\n";
}
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Output:

The tag is SOURCETAG
The tag is DATE
The tag is EDITION
The tag is HEADLINE
The tag is SOURCE
The tag is LINE
The tag is TTL
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