1)
Why did He say "Lamah Sarivu"?
1.
Rashi: How can you argue with Me, and say 'we did not sin'?!
2.
Radak: When the enemy comes, you complain and say 'why did Hashem abandon us, and give us over to our enemies?'
3.
Radak citing Targum Yonasan: Why do you judge against My words?
4.
Malbim: Why do you want Me to save you? You all sinned against Me, so I need not save you!
2)
Did they all sin against Hashem, even the Tzadikim?
1.
Rashi (from Bava Kama 92a): The verse implies so. This is like people say, 'in uprooting the thorn, also the cabbage is stricken.'
2.
Radak: "Kulchem" includes the great and small.
