Diesels---Marine vs Constant running

The salty marine environment is a large issue for gas, diesel, large and lil engines.
Varying load cycles and varying temp cycles in-between most of their lives of just sitting and condensing in a wet (salt) environment.
Imagine sitting around most of your life with warm salt air blowing up your exhaust pipe.
Your light craft marine engine is also tuned to output performance and horse power (consume lots of fuel).
Finally, ad the coup de gras; poor, cheap and intermittent maintenance by the owner.

I don't know about a Cummins 11L lasting 50,000 hours but compared to privately owned boat engine, the constant running engine (commercial gen-sets for example) runs at the same temperature, runs at the load per best design, serviced with stop-watch schedules with top quality materials.
These engines are also tuned for low horse power. Tuned to deliver it's best torque & economy at a set RPM that is a fraction of the light craft marine engine.
Along with a air inlet system way beyond the crude disasters of our marine engine, these constant running engines don't sit around most (any) of their life with salt air blowing up the out-lets.


Finally, your differences between models vs overhaul schedule is poorly measured in hours; but better defined in fuel consumed.
Your boats QSM11 can consume 60+ gallons of fuel in one hour.
That same 11L in a gen-set (loaded) takes 2 days.

In that same 2 days, the gen-sets oil is still clear.
The boats oil is black and stinks in 1 hour.