It is a good thing we don't follow this once a year thing with our vehicles
Quality bearings,
seals and the
initial service should be good for many, many thousands of miles and years. I have seen automotive wheel bearing with well over 100K of miles that looked fine.
That said, it seems the 3 things mentioned above are lacking on new trailers - every brand. So if you haven't had it done in 3 years, 10K miles, you might want to do an inspection.
My trailer had MOR/ryde IS and disc brakes installed when new. Last summer I had the "opportunity" to have some work done that required removing the hubs. I had planned on buying new seals and actually doing the bearings last year, Figured after 5 seasons and 20K miles it was time.
Glad I didn't, because the work that was done by MOR/ryde when new was still just as good and did not need any attention.