Stab trim is set for a TO with all engines operating. If there is a discrepancy in the stick pressure, you trim, unless you rely on speed trim. That accounts also for the unlikely event if you loose an engine.
Why would anybody in the world plan for a 2 engine take off, and set the trim for an engine failure case?
The different seat distribution, and actual versus calculated weights on a given station will most likely be the reason for the slight out-of-trim condition.