This has been discussed to death. Actually, several times (so it probably has 9 lives).
I don't mind if you enable the TFTD formula for yourself. But long story short, the 0-200% has several reasons behind it, but let me highlight the most important two:
1) Unit hitboxes in X-Com are always vertical cylinders. This means that they make a far bigger target than the graphics, and the common sense, would indicate; and also that a bullet will count as a hit even if normally it would go between the legs etc. the potential for low damage results is meant to counter this effect, albeit admittedly in a very approximated way.
2) The TFTD formula generally makes for a more dull game, with less excitement and more bean counting. Also it makes some balance decisions problematic (as in, some units may be very hard to kill, since you can't count on 200% "headshots").
Additionally, I should remark that many weapons in XCF have custom formulas, different from the 0-200% vanilla.