Why didn’t Abu Bakr bring the people together to pray Taraweeh in congregation, whereas ‘Umar did (may Allah be pleased with them both)?
Question

                Why didn’t Abu Bakr bring the people together to pray Taraweeh in congregation, whereas ‘Umar did (may Allah be pleased with them both)?
Praise be to Allah.
    Firstly: 

    An-Nawawi 
    (may Allah have mercy on him) said: Taraweeh is Sunnah according to 
    scholarly consensus.

    End quote 
    from Sharh al-Muhadhdhab, 3/526 

    Al-Khateeb 
    ash-Sharbeeni (may Allah have mercy on him) said: They (the scholars) are 
    unanimously agreed that it is Sunnah and that it is what is referred to in 
    the words of the Prophet (blessings and peace of Allah be upon him): 
    “Whoever prays qiyaam in Ramadan out of faith and seeking reward with Allah, 
    his previous and later sins will be forgiven.”

    Narrated 
    by al-Bukhaari.

    End quote 
    from Mughni al-Muhtaaj, 1/460. For information on its being 
    prescribed to offer it in congregation, please see the answer to question 
    no. 21740. 

    Secondly: 

    With 
    regard to ‘Umar (may Allah be pleased with him) being the one who first 
    brought the people together to pray Taraweeh in congregation, whereas Abu 
    Bakr (may Allah be pleased with them) did not do so, this question was 
    answered by Imam ash-Shaatibi (may Allah have mercy on him) in his book 
    al-I‘tisaam, 1/194, in which he said: Abu Bakr (may Allah be pleased with 
    him) did not do that for one of two reasons:

    1.
    
    either 
    because he thought that the people’s praying qiyaam at the end of the night, 
    and what they were doing, was better in his opinion than bringing them 
    together to pray behind an imam at the beginning of the night; this was 
    mentioned by at-Tartooshi;

    2.
    
    or it was 
    because he (may Allah be pleased with him) had little time to examine such 
    minor issues, when he was focused on dealing with the apostates and other 
    issues that were more important than Taraweeh prayer. Then when Islam became 
    well-established at the time of ‘Umar (may Allah be pleased with him), and 
    he saw the people scattered in the mosque, as it says in the report, he 
    [‘Umar] said: If I bring the people together to pray behind one reciter, 
    that will be better. When he did that, he pointed out that their praying 
    qiyaam at the end of the night was better. Then the salaf (early 
    generations) agreed that this was valid and they approved of it, and the 
    ummah cannot unanimously agree on misguidance. The scholars stated that 
    consensus can only be on the basis of shar‘i evidence. End quote. 

    And Allah 
    knows best.