You cannot compare most of todays sealed car bearing to trailer axle bearings.
If you burnt up a bearing and spindle after 3 years, I would immediately suspect maintinance. After that you could suspect other items, but in my history I have seen most people do not take trailer bearing maintinence serious enough. Yes the bearings should last quite a long time, but with long times sitting between heat cycles moisture can and will get into the bearing cups and foul up the grease. Even my little car trailer with 5k axles needs to be inspected annual but usually requires a complete teardown and repack every 2-3 years and its only used about 2-3k miles a year.
It does suck that this happened, and it should not have and the expense sucks. But I doubt anyone will cover much more unless you can clearly show that this was due to a manufacturing defect and not lack of maintinence.