1. The reason there are no ruku and Sajud in funeral prayers is that this is in reality not a real prayer because it does not have the requirements of a real prayer such as purity of clothes, body, and even minor ablution i.e. wudhu. In fact, it is a dua on the part of momeneen (believers) for the deceased.  Someone put a similar question to Imam Sadiq (AS) to which the Imam (AS) answered:

«سَأَلَ یُونُسُ بْنُ یَعْقُوبَ- أَبَا عَبْدِ اللَّهِ (ع)- عَنِ الْجِنَازَةِ یُصَلَّى عَلَیْهَا عَلَى غَیْرِ وُضُوءٍ فَقَالَ نَعَمْ إِنَّمَا هِیَ تَکْبِیرٌ وَ تَسْبِیحٌ وَ تَحْمِیدٌ وَ تَهْلِیلٌ کَمَا تُکَبِّرُ وَ تُسَبِّحُ فِی بَیْتِک‏»[1]

Yunus b. Ya'qub asked Imam Ja'far Sadiq about the permissibility of offering funeral prayer without wudhu. The Imam answered, "Yes, the funeral prayer is not but takbir (Allahu Akbar), tasbih (glorification), tahmid (praise), and tahlil (saying la ilaha illallah) in the same way as you say takbir and tasbih at home.
2. According to Shia religion, the funeral prayer consists of five takbirs. Those who offer the prayers testify, in the middle of the takbirs, to the oneness of Allah, the Exalted, and the prophethood of the Messenger of Allah (S) and they also send out greetings (salam) to the prophets, Ahl al-Bayt, the martyrs, the truthful and noble servants of Allah. Then they pray for the corpse on which they offer prayers. They pray and seek divine forgiveness for him or her.
For further details and information in this regard, study this answer: The Funeral Prayers, 21034

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