While laying siege to Hadhrat Usman (RA)'s house, Hadhrat Talha was reportedly the head of house guards and he did not let people, food and water in the house.

In this way, he took 'Uthman's revenge against Hadhrat Talha.

Afterwards, 'Abd al-Malik Marwan said, “Unless my father had told me that he has killed Hadhrat Talha, I would murder all Talha's progeny in revenge for Hadhrat Usman (RA)'s blood.”

Numerous sources have revealed Hadhrat Talha's strong enmity towards Hadhrat Usman (RA). Due to this very fact, Marwan Ibn Hakam, who stayed alongside Hadhrat Talha in the battle of Jamal, observing that the war was coming to an end put an arrow in the bow and killed Hadhrat Talha.

Hadhrat Talha and Hadhrat Zubayr were ranked among the most hardline critics of Hadhrat Usman (RA). Hadhrat Ali (RA) used to say about them, they are demanding of me a right which they have abandoned, and a blood that they have themselves shed.

حَدَّثَنَا مُسَدَّدٌ، عَنْ يَحْيَى، عَنْ حُمَيْدٍ، عَنْ أَنَسٍ، قَالَ قَالَ عُمَرُ ـ رضى الله عنه ـ قُلْتُ يَا رَسُولَ اللَّهِ، يَدْخُلُ عَلَيْكَ الْبَرُّ وَالْفَاجِرُ، فَلَوْ أَمَرْتَ أُمَّهَاتِ الْمُؤْمِنِينَ بِالْحِجَابِ، فَأَنْزَلَ اللَّهُ آيَةَ الْحِجَابِ‏.‏

Sahih al-Bukhari 4790

قَالَ كَانَ آخِرَ قَوْلِ إِبْرَاهِيمَ حِينَ أُلْقِيَ فِي النَّارِ حَسْبِيَ اللَّهُ وَنِعْمَ الْوَكِيلُ‏.‏

(1) The caliph was accused of religious heresy.
(2) Another objection to Hadhrat Usman (RA) was devolving upon people of the Umayyads governing the cities.
And
(3) The third objection of rebells to Hadhrat Usman (RA) was, his extravagant spending of resourses to the Umayyads' family.

There are so many reasons for rebelling against Hadhrat Usman (RA) mentioned in historical books.

Hadhrat Usman (RA) had never been a weak Caliph despite rumors & robustly handled the affairs from scratch. His murder by Prophet (S) 's companions & other protesters did not mean his lack of enough power but because the protest against him was so much that he & his companions could not control it.

#HadhratUsmanRA first action was to overlook 'Ubayd Allah Ibn Umar's punishment. He killed 3 people, Iranian Hurmuzan & Abu Lu'lu' 's family who were accused of murdering his father, Hadhrat Umar (RA). Hadhrat Usman (RA) as the ruler dispensed with his Qisas, retaliation & changed it to blood money.

one step down Hadhrat Abu Bakr (RA) and unlike them, Hadhrat Usman (RA) sat where Prophet Muhammad (S) sat. When he mounted the rostrum, Hadhrat Usman (RA) couldn't speak. He thought a bit and then, “you need a just Imam more than a lecturer”, he said. Then he came down the rostrum and went home.

As swearing allegiance to Hadhrat Usman (RA) ended in the last day of Dhi l-Hajja, 23 A.H., he sat on the Messenger's (S) rostrum. The difference between him and previous caliphs was that Hadhrat Abu Bakr (RA) sat one step down where the Prophet (S) used to sit, Hadhrat Umar (RA)

Hadhrat Umar (RA) had probably realized or practically had the inclination that Hadhrat Uthman(RA) was more capable rather than Hadhrat Ali (RA) of leading an Islamic society because of his influence and popularity in Quraysh.
#HadhratUsmanRA

In Hadhrat Abu Bakr (RA)'s time, he was close to him and was his scribe. It was him who wrote Hadhrat Umar (RA)'s allegiance - Abu Bakr (RA) said - while he was unconscious. Also, he had a great influence in Hadhrat Umar (RA)'s time and was the Umayyads' envoy in that situation.
#HadhratUsmanRA

He was one of those who migrated to Ethiopia, but soon he returned Mecca and migrated to Medina. There, he married two of the Prophet Muhammad (S)'s daughters respectively who died soon. Because of his wife's sickness, Hadhrat Usman did not attend the Battle of Badr.

Hadhrat Usman (RA) was one of those Muslims who became a Muslim as called by Abu Bakr in the first years. He was one of the Umayyads and his Islam was strange in a family most of whom were anti-Islam people