It takes a severe amount of material for satellites to pick it up with visual sensors. That silicate is very fine and floats in the upper atmosphere without detection. Fan blades of turbine engines suck up enough of it from seemingly acceptable air quality and become contaminated with glass adhering to the fan blades.
Agreed.
What it looks like happened in Europe was overreliance on computer modeling and not enough hard data collection.
The 2000 NASA flight was a considerable distance from Mount Hekla when it encountered the invisible ash cloud. Interestingly enough, that plane wasn’t damaged as severely as it could have been due to the ash particles being coated in ice.