Eruvin 75a - Regel asurah bimkomah

In the gemara Eruvin 75a, and a number of other places, there is a principle רגל האסורה במקומה אוסרת שלא במקומה “regel ha’asurah bimkoma oseres shelo bimkoma”: A “foot”/person that is forbidden [to carry] in its place, also forbids outside of its place - meaning that someone living in an inner courtyard, who must pass through an outer courtyard to get out, will forbid the outer courtyard’s eruv if he is not allowed to carry in his own inner courtyard. Otherwise not.
There are two other opinions there, Rabbi Akiva and a third tanna. Rabbi Akiva holds that even if he is permitted in the inner courtyard, he forbids the outer courtyard. And the other tanna holds that even when he is forbidden in his own courtyard, he still does not forbid the outer courtyard.
I find these last two opinions easier to understand – Rabbi Akiva can just say that since he has to pass through the outer courtyard, he is considered one of its inhabitants, and will forbid its eruv if he doesn’t join it. And the other tanna can say that he is not considered one of its inhabitants, so it doesn’t matter what he can or cannot do in his own courtyard.

But what is the idea behind the middle position, which we see in the rest of the masechta and the Shulkhan Arukh? Why does it matter whether he can carry in his own courtyard?
It seems to be a takanas Chazal, so presumably there must be a logical explanation for how they set it up. What is that?

Now I see that the gemara and Rashi actually give an explanation for this, 59b.
"The inside courtyard can close its door and use things there - since it is mutar in its own place, in such a case we force people 'not to emulate Sedom': they must do kindness for others if it doesn't greatly inconvenience them themselves. For one day they can give up the ability to trod through the outside courtyard. Just let them close the door and use their own courtyard."