Why was hadith not taken from some individuals described as maʾmūn?

Isnād as Part of Religion: Transmitter Competence, Fitnah, and Connected Transmission

• They were personally trustworthy but not established as sufficiently skilled transmitters
• Every report from them had been proved fabricated despite their upright character
• They transmitted by meaning, making each narration necessarily inadmissible
• Any isolated disagreement with other transmitters was deemed sufficient for universal rejection