Because it is more trouble than factory EFI, with no reallakotastoy said:O.K
The Projection sure gets a lot of grief from you folks.
advantage over factory EFI!
I don't know how the Projection could be that much easier to trouble shoot than Ford EFI... a cheapo code scanner, fuel pressure tester, a couple of relays, and a spare TFI and you are set for most trailside problems. The whole point of EFI is so you don't have to screw with it! If I wanted to fiddle around to make the motor run right I'd save money and run a Holley carb. Factory EFI simply works right off the bat, no messing around. The big advantage with the factory EFI is there is ALOT of performance support for it so if you do want to upgrade there's plenty of stuff out there to do it with.
Secondly, yes the the factory EFI is a nice conversion and certainly the most reliable for EB's but this is in part due to the fact that you don't really have to know what you are doing to get it to work right. It is already tuned and set up for your engine. The projection system will run great but only if you fully understand the system. This is by no means a plug and play installation.
You are better off with a projection if you want to better troubleshoot your fuel system if problems do arrise. In terms of performance...well you gotta find out for yourself. Go for it. Live a little and learn a lot. I'm happy I did on my 72' EB!