> Do runways have some sort of barrier between them and the next "important" thing.

Some do. Here is what it looks like when an overshooting plane utilizes such a barrier: https://www.youtube.com/watch?v=zW71FrX8t_g

179 dead.

Consider the possibility that gigantic flying aluminum tubes filled with tons of flammable fuel hurtling around at hundreds of kilometers per hour comprise a dilemma that has no trivial answers. Even defining what "important thing" means at any given instant is not straightforward.

There is a spectrum between "no barrier" and "immovable barrier".

Arrestor beds exist, and given enough space a fully loaded plane at take-off velocity can be stopped in a controlled and safe way.

Cost and space are often the reason why this does not happen.