Headphones tend towards being fragile by their very nature.
First, just about every headphone has a tiny, thin wire leading
from the headband to the earcups. Some manufacturers
leave this exposed (Sony MDR V6, Shure SR 840,
Beyer DT 880) but most protect it with some sort of
covering. Still, that covering is almost always
thin and light (see 'comfort' below).
Thus, the weakest link on headphones is very weak indeed.
Second, you've got parts that move - gimbals, hinges,
etc. - and those parts just can't be produced with
great bulk and solidity.
Third, comfort is very important in headphones, so
they're most often made of plastics and polymers
which don't have tremendous strength. Some strength
is exchanged for lightness and comfort. Obviously,
no one is going to make a set of headphones out
of - for example - steel without moving parts.
Some headphones are pretty durable as headphones
go. They tend to be inexpensive.