If you could, you probably wouldn’t also be continent of faeces!

But this gives a lower seiza.
If you relax, yes, but ‘martial arts’ seiza is supposed to be an ‘active’ position with the quadriceps tensed so the buttocks are held above the heels rather than sitting on them. Many people sit with the shoulders and upper body completely vertical or leaning backward, the navel pointing upward. This position is incorrect for tactical purposes an and is a relax position to have a cup of tea, Obaasan-style, that is Grandma style! The samurai way of sitting should be with the navel pointing horizontal or downward to the ground and the shoulder/upper body
slightly leaning forward, ready to take any forward action needed. For swordmen, a good indicator of a wrong position is to check that in sitting position the sword’s tsuka (handle) is horizontalish or rather, not pointing
excessively upward.
Some practitioners sit down in seiza ‘Obaasan style’ and a moment before the kata begins, engage the ‘active position’ rising slightly to indicate aggressive intent.
Just before practitioners
When I look at other kyokushin mates, I think some of them probably do it properly, but not all, as they have trouble with it.
Many Westerners don’t have the flexibility in the quadriceps to sit in seiza. Sometimes I even see Westerners sitting uncomfortably cross legged with their knees point upwards in a ‘V’ shape because of tight leg adductors; not good.
But I have never had an instructor order the class everyone pushups because someone fails to to this properly.
Such a funny way to treat adults!
Sometime that does happens if many forget the kiai, lack dedication or if noone acqknowledge instructions with osu.

Isn’t it better to point out the error so it can be corrected? Admittedly serial non-compliance should result is a moderate beating with thin hazel twigs.
Ah, this is an argument of logic - if it holds, as it applies to efficiency of fighting, at least in theory, I buy it any time of day! over pure aesthetical arguments.
Yes, one can move in all directions from tate hiza but from seiza it is harder to move to the sides or indeed, backwards.
I like to think (or wish?) that they can be unified. Ie. that the "art" part is the preferences for "perfection" of at least theoretical effective robust in fighting, as I don't plan to actually engage in right fights (except in the dojo of course).
Some movements are merely vestigial. A backward sweeping motion of the hand over the sword handle means nothing now, but it was originally to flap long sleeves out of the way so they weren’t grasped with the handle. A curious returning sweep of the right foot to the starting position at the end of a kata (like this ¿) was to sweep away a long hakama hem so you didn’t get you foot tangled up or step on the hem.
But we never really practiced the scenario of uke starting in seiza when tori is attacking. That could be interesting. But maybe it's because there is no ground fighting. I assume this would be more relevant for ground fighters? or samurais as you mention?
We had these kata in Wado Ryu. They were great fun!