Surprised you have to ask why!
Great post and have seen both sides. Often it's about keeping quiet and protecting the image whether the airline, manufacturer, regulator or mates.
often based on ignorance.
From losing a best mate with a known problem which was kept secret on an aircraft that had been in service for a decade to two aircraft I transitioned onto in the first months of commercial service.
It includes software problems, structural deficiencies and the books being wrong.
The average line pilot working his socks off has to rely on the training department and they on the manufacturer/authority.
Trident, DC 9 50, MD 80, 747 classic, DC 10, Fokker 100..all of which I had some deficiencies which some crews knew nothing about...flown all ...