Why does the Quran mention Lot's call to his people to abstain from indecency, without mentioning his call to "There is no god but Allah," as is the case with other prophets?

Lot, peace be upon him, called his people to monotheism and the worship of Allah, and to avoid polytheism, just like all other prophets. The evidence for this is Allah's saying: (And We certainly sent into every nation a messenger, [saying], "Worship Allah and avoid Taghut") An-Nahl/36, and Allah's saying on the tongue of Lot: (Will you not fear Allah? Indeed, I am to you a trustworthy messenger. So fear Allah and obey me.) Monotheism is the first thing by which a servant fears his Lord. As for the absence of an explicit text in the Quran stating his call to his people with the words: "Worship Allah; you have no deity other than Him," perhaps the wisdom is to draw attention to the heinousness of the act of Lot's people and their violation of fitra (innate disposition) and Sharia by lustfully approaching men instead of women.