PHP regex not working - parsing {{tags}}

What I want to do is parse the next line in such a way that all placeholders inside {{}}

are replaced with the value denoted by "default". For example, it {{time, default=noon}}

should become noon

.

Here is the code I tried:

$input = 'It was a {{color, default=black}} and scary {{phase}}. As the {{animals, default=dogs}} {{make_sound, default=barked}} and the trees swayed {{setting, default=to the breeze}}, a {{size, default=}} {{monster, default=troll}} that emerged from the shadows.';
$input = preg_replace('/\{\{.*default=(\w+)\}\}/i', '$1', $input);
echo $input;

      

        
        
        
      

    

Output Output: Output: It was a troll that emerged from the shadows.

Why are the remaining templates not processing correctly?