I am using a brake system as an example because it is a pressure system with no loss of fluid and no leakage. When you push the master cylinder you get a few cc of fluid movement through the system to move the brake pads. After they make contact you are building pressure because there is no place for the fluid to go, so in this system you have pressure with no leakage or flow.
An engine is not like that. Although it has pressure, because there are leakage points, you will always have flow to those leakage points. You have pressure because the volume coming in exceeds the leakage going out. In our example of oil velocity running past number four main in a stock system, occurs because there are too many leakage points beyond the first main bearing we need to feed.
Number four main is starved because there is not enough other restrictions to force the oil to go there. Front oiling imho would have two opposing pressurized columns canceling out much of the flow in the galley.
Because it is under pressure from both ends, that pressurized oil has the main bearing passages as its only place to escape.
Put another way, in the sealed brake system, if you blew a line while the system was pressurized, that would be the first place the fluid would leak from.
