Why are the keys laid out in a random order? So typewriters didn't jam. Typewriters also had positive tilt and both 'standards' have remained because that's how it's always been, not because they are good.
Which angle is best for you? Well that would depend on your setup - if you can achieve the magical knees at 90 degrees, elbows at 90 degrees and head level with the top of your monitor you would want a different angle than if, like me, your forearms are at a greater angle (sloping down towards the desk) If your chair is lower compared to the desk so your arms slope upwards you'd want a positively inclined keyboard to match.