Uchi komi - moving & static

For as long as I've studied judo, we always practiced uchi komi from a moving paradigm, albeit a small movement. Usually, once tori and uke hook up for, say, o soto gari, and then uke moves his right foot back and forth, while tori moves his left back and forth. When uke steps forward, we step on the line and fit in.

I couldn't help but notice over the years, that from what I could see of the rest of the judo world (which isn't necessarily a lot), everyone else practiced uchi komi with uke remaining absolutely stationary. As I understood it, the main reason for practicing uchi komi with uke stepping was simply because, when we're actually doing randori, we're both moving. It would seem logical that we learn to time our movements to that step.

So why did the rest of the world practice it static? (And did they all completely avoid moving uchi komi?) I don't really know. Is there any benefit to practicing it static as well as on the move?

Lately, I've noticed that there are times when I'm by myself, perhaps outside keeping an eye on my son as he plays, or any other moment where I'm standing around waiting, that I'll be thinking about judo and will practice a particular set-up alone. I'll practice pre-turning my foot, making sure my hands or elbow are doing what they should, etc.

I realized that I'm more or less doing a static uchi komi, just without a partner (or a tree trunk, as in some examples I've seen). The only thing that troubles me from watching videos like the one above, is how tori, once he does the fitting in, will then often return not to an upright posture, but bent forward with one leg thrown back as if to gain momentum for the next entry.

I'm no judo expert by any means, but to me, bending forward and throwing your leg back seems kind of like a bad habit to practice. I would think that tori ought to return to a more upright posture, with both feet under his butt.

I think I'll throw this question on the forum and see what response I get.