not knowing what the axle will be used for may be part of the repack recomendation. Boat trailers that get in the water one story. Travel trailer that gets used often, another story where you can probably go a long time between repack. Then there is the person that takes the trailer out once/year for 2 weeks and then it sits out for 50 weeks. probably not good for bearings either.
I repack a new trailer axle at one year then let it go at least 5 years. My neighbor has put close to 200K miles on his cargo trailer and 150K on the previous cargo trailer and never had a failure and never did a repack either. They get 30K ish miles/year.
Our son's work cargo trailer probably has 75K on it, about 10 years old, never been repacked, no issues.