Simply put, the third (g) string has MORE TENSION than the others on a steel stg. guitar. Guild owners know this all too well, as Guild specs call for a longer scale length (More tension at std.pitch). With nylon strings, the fourth(d) has the most tension. Of course, sharp edges, poor installation, and heavy bluegrass g-runs can take a toll as well.
    Buy the way......plastic coated strings from any maker do not "last" longer, unless you are of the few that have very corrosive bodily fluids on your fingers. Strings lose their tonal quality due to work hardening. Change tunings often, play hard.....Help the string industry