The way this bulb broke but stayed lit.

because modern bulbs dont need the outer pear-formed glass housing. The outer glass housing is mostly for aesthetics to keep the form traditional. What actually glows is a more efficient, downscaled glass body which is the part that stayed alive in your picture

Looks like a Halogen bulb that are replacing the older incandescent. The outer glass bulb is there mainly to replicate the appearance of the older bulbs, but also there as a mandatory safety mechanism. Halogen bulbs are more efficient than older incandescent technology, but have the slight drawback of having a tendency to "explode" when they finally go bad so all fixtures designed for halogen bulbs have an extra layer of glass between you and the bulb. I dont mean it will take out a room or anything, but can send small bits of glass flying. I used to work for an outdoor lighting company when halogen bulbs like that first started to appear and we had to test them to failure. We tried to accelerate the process by weakening the glass and I caught a small chunk of glass in my neck as a result. Nothing worse than nicking myself while shaving, but still kinda scary.

if this years anime taught me anything its that the outside glass on bulbs is only to provide a vacuum so that no oxygen can get inside where the filament is, since having oxygen present would cause it to burn too hot

Always stay lit