It's also to keep the All-but-one principle in-tact when possible. As others have stated, if you want holding to be previous spot, then you have to make an exception to the rule. But then, if you have holding in the end zone, you don't want that to be previous spot, you want that to be a safety. So you have an exception to the exception (which is the original rule). Then you have to make it clear you only want this to happen prior to a change of possession.
So you can see how complicated it can get. All but one is simple.
I've proposed changing what the basic spot is to help alleviate it somewhat. I proposed that if the run ends behind the neutral zone, the basic spot is the previous spot. This helps with defensive fouls being enforced from the LOS, but offensive fouls still will be spot fouls. The change is mainly to clean up the definitions. So basically the only time you have a loose ball play is on legal passes and kicks. No distinction when you fumble behind or beyond the LOS. They're all RUNS! Simple.

Fully agree, Bossman, we've tried to pass this several times but with the objection of doing away with A-B-O on fouls behind the LOS on A along with it. This occurred sometime in my murky past :
(1) Early in the game, on 1st down, visitor's QB sacked 17 yards behind LOS by PFFM;
(2) penalty made situation 1-12, visitor's coach call time and wanted me to explain;
(3) I said : "Even though the play netted a -2, it's better than a -17 AND you got to replay the down !"
(4) Coach accepted my explaining;
(5) 3rd period, home up 30, scrambling home QB grabbed by PFFM and fumbles 10+ behind LOS, B recovers;
(6) after informing U to begin his trot from LOS, I felt obliged to inform the V coach of the diff;
(7) I approached the coach and began : "....Coach, I want to explain the difference....";
(8) you can get away with a lot more with a

than a

...Coach : "Oh, I know the difference,

this was the HOME QB

!"
(9) I responded, with a

, the difference;
(10) He returned : "It's a bad rule, isn't it? "
(11) I agreed : " In this situation, YES, BUT IT IS THE RULE."
(12) He accepted that and said : "We're getting crushed by BAD blocks, BAD tackles and BAD PLAYS; NOT by bad rules. You guys are doing a good job. Keep it up."
IMHO, both fouls along with fouls by B downfield when A is sacked behind , should carry previous spot enforcement....BUT not at the cost of adding exceptions to our A_B_O.