Thyme infusion - Cointreau vs syrup?

After reading through the instructions (twice), I’m going to make a guess. I bet it has something to do with getting the most bang for your buck for the least work. By that i mean, if you soak it in the booze and strain it after a week, you can keep that indefinitely, no fuss, no muss. If you did it in the simple syrup (which i see nothing wrong with), then you’d have to sterilize the jar for long term storage and have a lot more to worry about with bacterial. Alcohol will take care of that concern. I still think you could do it the way you’re asking about, but maybe use it up within a week or so.
This is just my guess on the matter.