Trailers age parts wear out and metal fatigue is a fact of life. I have had a wheel snap off the axle once and it gave no signs it had a problem. I have had the bearings fail on a wheel once and it wouldn't have driven another 1000 feet when it did. Again no signs there was a problem till there is one. I have had an old lady merge into my trailer once and bend an axle.
In all cases the trailers had dual axles and in all cases were able to limp home after being unloaded into one of our other trails on 3 wheels. It's nice to have that ability and if you had a single axle in all 3 cases you'd be getting a flat bed and a nice bill plus the loss of your day.