I teach these basic transformations as part of my middle school math classes, and I was completely loss as to why they didn't include a reflection, but then I realized a reflection wouldn't be that interesting because it could be indistinguishable from a translation.
Scaling, in general, is the least common middle school transformation covered by state curriculum as far as depth of knowledge is concerned, at least where I've taught. Students just aren't ready at that age to calculate something as sophisticated as the scale factor contributing to an object's loss of size.
I think the students are ready and quite capable of such sophistication. They're just too distracted with sharing memes.
(Oh, I know, my middle schoolers do alright as long as our figures are two-dimensional, and my high school geometry students do very well; I just wanted to say the magic, fun, wink wink word again. 🙂)