"The imaging looked like a field of stars - a Milky Way of tiny cancers..."

[ProfessorGAC]

3. They Underestimated The ....

...frangiblility of asbestos back in the day.
Even after the danger was known, they decided to make sure the pieces were big.
They greatly underestimated the ease with which big pieces could be ground, in normal use, into microscopic fibers.
Of course, it gets worse. When they knew both the danger & the easily frangible nature of asbestos, the manufacturers simply buried the data.