First and foremost: Why on earth does our PC getting KO'd end combat?
The boss wants the champion's contribution to the party and by extent battle to be paramount -- you are the only one with the flexibility and power compared to your far more static companions, and in that sense, carry your party. There is also the matter of player-only control being the default battle style and the only battle style early in the game's life; he didn't want people sitting at the screen watching autocombat complete, nor be overly carried by their companions.
While there was some disagreement in the core dev team about this decision, he had the final say in this and we've fallen in line in the years since then.
Second: Why are the stats we are allowed to rank up tied to our background?
The boss wanted one's background, race and class to have some minor meaning without being overly restrictive. The three sets of three each provided would provide reasonable coverage of most stats while only extreme archetypes would have more than one stat blocked.
Respec exists to correct that, at a small fee.
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These decisions have been discussed in the past at considerable length, and are unlikely to be revisited any time soon. While I'll never say never, I wouldn't hold my breath for changes, especially since we just looked at reworking the tutorial and some basic systems not too long ago.