Maybe you're just noticing all the poly breakups because of your headspace. It's not like all the monos are doing such a bang-up job of it either...
My question is... why the attachment to poly identity if you don't feel it's working? Poly is just a label. There's no point getting attached to a label if the associated behaviour and feelings don't flow naturally.
Focus instead on what you'd like out of life, what your needs are. Then look at strategies to meet those needs. If poly makes sense as one of those strategies then giv'er. But either way, just do what feels right for you.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker