I don't disagree that they'll eventually break, but we've made many
hundreds of launches before a fatigue. When we have broken two at a
time due to a gust load, we replaced them with two new ones. Next
launch we broke both again. We were launching into strong winds with a
shear about 500ft. Over time we have broken the wire much more often
than a weak link failure. Since we train for the proper response to a
launch failure, it no longer makes much sense to use up two at a time.
It does eliminate the potential for mis-assembly.

Frank