Welcome to my Leather 'Collector' Club Membership does not require you to wear them, simply to buy and stick in closet! Occasional trying on is required (oh, I see you're already doing that), as is occasional guilt and selling off of those demoted by new purchases (oh, I see you're already doing that too . . . ;-)).
I can only project my semi-formed ideas on why we do this. We LOVE leather! I know I love the feel of squishy, chewy leather. I love the smell of good leather. I love the way leather feels, the same way I love a really well knit sweater. Both should hug you just right.
Regarding failures, some of this must be your evolving style. #1-3 are highly styled and you've moved on. You also can't depend on lots and lots of jacket wearing weather to put them through their paces (i.e. #6-8).
In your success #4, I see that super flattering fit, the bright light color, and a style that is more classic/enduring. #5 reminds me of your new Burberry, and those earthy tones work beautifully on you, and really wears like an overcoat so it doesn't need extra styling.
I wonder how much of the success of #9-10 will be in being able to be worn open, unzipped. Just thrown on as a topper, not always as part of a styled outfit.