What would the wise say about this?

Good morning, Rabbi.
In your series on innovation and tradition, you talked about how one of the things that characterizes the Modern Orthodox is that it also makes considerations of value change within its halakhic considerations. That is, there is a certain ruling that can stem from some value (or a hidden value to which the poskim were not aware at the time of the Gemara), but if they were in today's reality, in light of the awareness of different values ​​(the status of women, for example), they would also rule in this way.
But, after a few chapters you talk about a ruling by Rabbi Moshe Feinstein regarding the Sabbath clock, where he says that if the conditions were here today, they would certainly rule it out, and you determined that it is not legitimate from the point of view of establishing halakhah.
I wanted to know what the difference is between the two cases? Why is it legitimate in the modern sense but not in the forbidding sense? (I assume this is not exactly what the rabbi claims. I would be happy to discuss the differences.)