By understand - what I really mean is that I presume that they couldn't get the game to work satisfactorily with a pad with those features in . If that is the case - which I think is the only logical explanation - with pad users being the target audience for this game, then they had to come out.
Tire wear and fuel have nothing to do with that.
I can explain for non-pad users.
In PCARS2, with my settings, some cars allow small course corrections while others eagerly jerk left and right. You can limit the steering according to how fast you're going with Speed Sensitivity to combat this, but then you cannot countersteer enough to correct a slide -- the driver simply will not turn the wheel far enough. You will only get the opposite lock you needed after you have spun and lost all your speed. You must either accept extra-sensitive steering or having your hands tied behind your back if you get sideways.
It's a poor compromise and rudimentary by comparison to most other console racing games, regardless if you have fresh tires, a full tank, worn tires, an empty tank, hot tires, cold tires, or perfectly warmed tires.
Wheel users often assume analog stick steering must be like driving a remote control car, and expect it to be inherently extra challenging. That's unnecessary, because developers figured out years ago that it is more effective to simulate the feedback that is missing.
A limit on turn-in simulates the feedback that you are on the edge of front tire grip, akin to wheel feedback going light. If you don't get as much steering angle as you expected, you know you are carrying too much speed. Countersteer can simulate the feedback of self-aligning torque, which I know firsthand is a guiding force on FFB wheels and in real world oversteer. The neutral stick position doesn't necessarily have to mean "straight on" -- Opposite Lock Help in PCARS2 simulates an effect similar to relaxing your grip on the wheel.
Uncoupling countersteer from the rudimentary Speed Sensitivity feature would allow turn-in to be tamed and managed independently, eliminating the compromise PCARS2 asks players to make. This is probably more or less what SMS finally figured out for PCARS3.
I've mentioned more than once before why I think SMS did what they've done:
As for PCARS3, I don't believe anything it has given up was for the sake of making the game more playable with a controller, per se. To the extent that it is about accessibility (I suspect SMS also found it quicker and easier to polish), it's just to make it more accessible in general -- not requiring players to think about cold tires, brake heat, brake ducts, proper tire compounds for the weather, fuel/pit strategies, or making sure you got the tires you expected from a pit stop.