That makes sense ... and since you've done it several times before, it probably weakened your pliers over time. Any time you bite into something with pliers and use the wire cutters and you have to use a bit more force than usual, you are pushing the two plier blades outward not towards each other.

That is why I was curious as to why they broke ... if you had tried gripping something with so much force that it broke one of the plier jaws - the jaw or the handle would have been bent out of shape first before the jaw would break .... (ask me how I know because I've done it before with a pair of vice grips)

But if you tried using the wire cutters and put force behind it while trying to cut something solid like a screw, then you are no longer pushing the plier jaws together, you are moving them laterally outwards ... and if you do that enough times, eventually the jaws will break .... (ask me how I know that because the more I analyze all this, the more I remember that I have broken pliers and wire cutters this way before)