Bildad had made his view clear: God looks after the righteous and punishes the wicked. Therefore, Job must have done something wrong. If not, then just using logic, Bildad could say to Job:
Job 8:20-21But look, God will not reject a person of integrity,
nor will he lend a hand to the wicked.
He will once again fill your mouth with laughter
and your lips with shouts of joy.
Although this was eventually true for Job, the problem was that, as Job said, there is no one righteous enough to take on God:
Job 9:2-4 Yes, I know all this is true in principle.
But how can a person be declared innocent in God’s sight?
If someone wanted to take God to court,
would it be possible to answer him even once in a thousand times?
For God is so wise and so mighty.
Who has ever challenged him successfully?