Why can't 去 or 回来 be used with 在 or 正在 to become progressive
The answer is "habit".
Because we don't write or talk in that way.

For example, both 肥 and 胖 mean "fat".
We call a fat person as 胖子.
肥子 is not usual because we don't have the habit.

He is going to school.
We translate it into 他在去學校的途中.
We don't have the habit to say 他在去學校.

That fat guy is going to school.
那胖子在去學校的路上。
??? 那肥子在去學校。 ???

Besides 去 and 來, 返, 歸, 往 and 到 are also included.
These verbs are used together with something like "on the way (途中／路上)" to express the progressive tense.

回 is acceptable. For instance,
Q: "他有沒有回電話？" (Did he call back?)
A: "他正在回。" (He is calling back.)