Surah of At-Tur verse 24 Ghilmanun Llahum K'annahum Lu'lu'un Maknun. Why are we promised attractive boys?

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Beauty of a spouse, palaces, rivers, fruits and so on demonstrates Allah's perfect favor on His believing servants.
Know that Allah, The Exalted, has purified the hearts of believers in Paradise. Allah Says (interpretation of meaning): about the people of Paradise: {…You have done well, so enter here to abide therein."} [39: 73].
In the same vein, the Prophet (Sallallahu Alaihi wa Sallam) said: "The inmates of Paradise would eat and drink but would neither spit, nor pass water, nor void excrement, nor suffer catarrh. It was said: what would happen with food thereupon the Prophet (Sallallahu Alaihi wa Sallam) said: 'They would belch and sweat (and it would be over with their food), and their sweat would be that of musk and they would Glorify and Praise Allah as easily as you breathe'" [Reported by Imam Muslim ].
Allah knows best.