Provided that the oil filter of an engine would be swapped every x time intervals as needed to be kept clean, I was wondering if, instead of removing all engine oil and replacing it with new (clean and uncontaminated), there would be any advantages in adding clean oil in shorter intervals and bleeding the same amount of the dirtier oil (probably left in the bottom most of the oil pan). This suggests that no oil leaks and oil consumption takes place. Would such a method provide better cleaning/flushing of the engine parts? The idea here is that replenishment will keep oil in an overall good/clean condition. If this method keeps the oil at an overall "cleaner" state would it help to prolong the filter longevity as well???
The short answer is convenience. It's just too much to ask of the average consumer to perform a drain-and-top-up procedure at regular intervals.
It's also messy. Anyone who's topped up oil without a funnel can attest to that. And once the drain plug is undone, you can't turn off gravity at will to prevent spills.
Some manufacturers do this - at least on larger equipment.
The oil is rated for 100,000 miles and the filters changed every 10,000 or 20,000. The oil is topped up as necessary. And, in some locations they are very quick to sort leaks so they don't contaminate the terrain...
I did this on a car kept the fully synthetic in for twice the recommended interval but changed the filter as per spec. Engine was fine, but I was using Mobil 1 5W-50 and it was really expensive then.