The sun delayed for others after this, e.g. Chizkiyah!
Radak: The verse says that such a miracle will not happen again via someone's prayer. 1
Malbim: (a) Other miracles are due to Hashem's desire, or via a Navi's Tefilah. Here, Yehoshua decreed! (b) Other miracles are to aggrandize Hashem's name, or to elevate Yisrael, or to save Yisrael. Only here, it was to show that Hashem fights for Yisrael.
We find that the sun reappeared after it set, in response to the prayer of Nakdimun ben Guryon (Ta'anis 19b)! There, it was not an overt miracle; people could say that the sun had gone behind a cloud, and seemed to set. Alternatively, Nakdimun did not explicitly ask Hashem to make the sun appear again. (PF)
