Look, the windows not supposed to fall off, for a start. These things are built to rigorous aeronautical engineering standards — cardboard’s out, cardboard derivatives, no cellotape, no string. So chance in a million, really.
And to be clear, the plane that the window fell off was flown to safety. So there’s nothing out there but birds, air, wind and clouds… and the window that fell off.
"debris from a dramatic engine failure caused damage to the aircraft's window"
That's high-velocity pieces of metal. Hard to prevent that from shattering a window if engine housing didn't catch it.
How much stronger, thicker & heavier you want to make those windows? Costing how much more fuel? To save how many lives per year?
I'd think airplane builders (note: not airlines!) are more qualified to make that calculation than armchair safety 'experts'.
Turboprops can't, of course, contain a propellor failure which is why they have a big slab of armour in line with the prop disk. So in that case, yes, safety wins over cost and weight.