Why does the imam say the takbeer in the Eid prayer?
Question

Why is it Sunnah for us to say ten takbeers in the Eid prayers before reciting al-Faatihah? What is the benefit of that, and why do we do it in these prayers and not in the five obligatory prayers?
Praise be to Allah.The basic principle concerning acts of worship is to worship in the manner enjoined by Allah and His Messenger (peace and blessings of Allah be upon him), whether we know the reason behind it or not, especially in the case of prayer, fasting and Hajj. Reasoning has nothing to do with it. This includes the six or seven takbeers which the Prophet (peace and blessings of Allah be upon him) prescribed following the opening takbeer and before the recitation of al-Faatihah in the first rak’ah of the Eid prayer, and the five takbeers before the recitation of al-Faatihah in the second rak’ah of the Eid prayer, but not in the five daily prayers. 
We must believe in what Allah and His Messenger (peace and blessings of Allah be upon him) have prescribed, and submit to it; we should hear and obey, because the basic principle in this matter is to worship Allah and not to look for reasons.  
A person has no right to interfere in matters that are the unique preserve of Allah, such as worship and what kinds of worship are to be done and in what manner. He should not ask why has Allah prescribed some things and not others, or what is the benefit of this that He has prescribed. Rather he should learn what Allah and His Messenger (peace and blessings of Allah be upon him) have prescribed, and act in accordance therewith. If the reason behind it becomes apparent to him, then praise be to Allah; if not, he should submit to the rule of Allah and obey Him, and have certain faith that Allah has only prescribed things for a reason and in the best interests of his slaves, because He is Most Wise and All-Knowing in all that He says and does, prescribes and decrees. Allah says (interpretation of the meaning): 
“Certainly your Lord is All-Wise, All-Knowing” [al-An’aam 6:83]
What we have said is supported by the verse in which Allah says (interpretation of the meaning): 
“Indeed in the Messenger of Allah (Muhammad) you have a good example to follow”
[al-Ahzaab 33:21]
And the Prophet (peace and blessings of Allah be upon him) said: “Pray as you have seen me praying.” Narrated by al-Bukhari in his Saheeh. 
And he (peace and blessings of Allah be upon him) said during his Farewell Pilgrimage, “Learn your rituals from me.” Narrated by Muslim, 378. 
And Allah is the Source of strength.