newcomer and all interested:
The questions you asked seem to be eternal. I don't believe we ever find out the reasons "why" to the same extent as we discover "what" works and what doesn't.
This is particularly true in systems.
In my case, I'm only an old chap off the side of the road, but, I've studied and paid to study racing systems for decades. Well over a thousand of the goddam things!
Since Christmas, I'm not afraid to admit that I've lost hundreds of pounds on live experimentation with hare-brained schemes I've thought up from various data.
And what did I find?
Well, if I'd stuck rigidly to a simple method involving Inform Racing's top -rated - similar to Martin K's trial - I'd be a few quid up by now.
Don't ask me why, 'cos I don't know!

I thought I knew better.
It could be a genetic weakness in myself; for instance, I'm so contrary, that I refused to get a new hip for ten years or more, preferring to hobble about in agony, rather than get the thing done with just a couple of days in hospital.
I thought I knew better than the specialists. Tried all manner of crazy diets and exercises: used to go to the gym twice a week and dancing three times a week. I was useless and it was painful.
How stupid I was! The simple X-ray was the correct indicator all along. I went to private clinics go leor to get all sorts of differing opinions. All a waste of time and money.
The old NHS X-ray was correct - as was the surgeon.
In conclusion, all I can offer is
do whatever works.
I mean, I don't even know why just one favourite in three wins in the long-run.
This recurring fact seems to be universal in both horse and dog racing. I could never find out why, but the fact remains, decade after decade.
Maybe there ain't no perfect answers in life?
Good luck to all!