I've actually asked this question to Bruno Cathala in the YouTube comments of his presentation video for the game. He seems pretty set on applying this rule to avoid the last few moves being tame.
I agree he is a great boardgame designer and Im a huge fan of 7WD. But he is, to my knowledge, pretty new in the world of Abstract games. And this rule does not make sense from an abstract point of view.
He mentionned that he likes the simplicity of the rules (pureté in French), but this extra rule actually breaks that simplicity in quite an arbitrary way.
The fact that the last moves are almost forced and that there is very little choice is a feature of every combinatorial game. Think of connect 4, Quarto, Othello, etc. Anticipating how the endgane is going to happen is part of the play. Once you get there, either you took an advantage by creating lines of 4 or inserts that will win you the game, or your opponent has, or you both have and you fight to be the first to get a free move, or none of you did and the game ends in a draw. That's what abstracts are about : reading deeper, anticipating further, exploiting early advantages in the late game.
Btw, I have a very nice idea for an advanced, purely abstract, variant of the game I believe. Instead of rings, use rings that are stroke by a line. Every time you play, chose the orientation of the line to force your opponent to play along that line instead of that being decide by the board. I think it might work.