If you think the “stack” is at all similar, you really have no idea how these things work. They’re fundamentally different, and throttle is drastically simpler than a steer by wire system.
Let's roughly sketch out what each stack has to do:
Sterr-By-Wire:
-- Read steering wheel position as input
-- Observe current vehicle speed (wheel rotation) as input
-- Read current steering 'feel" option chosen by driver
-- Compute desired rack position
-- Drive rack actuator to desired position, with appropriate ease-in/ease-out, taking into account vehicle speed as needed
-- Monitor rack position (preferably using dual independent sensors for redundancy and safety)
Throttle-By-Wire:
-- Read accelerator pedal position
-- Read brake pedal position
-- Read current throttle options, including mode (chill, sport etc), regen setting, creep/roll mode etc
-- Observe current vehicle speed (wheel rotation) as input
-- Compute desired acceleration profile based on all these settings
-- Control inverters on motors to map desired profile to torque, taking into account speed and driver options
-- Handle blending front/rear motor torque
-- Handle torque vectoring based on wheel spin
-- Apply brakes as necessary for additional torque vectoring for vehicle stability
-- Handle seamless transition from acceleration to regen (flipping inverter modes without creating jolts to car/occupants)
-- Handle creep simulation if enabled
-- Handle coasting simulation if enabled (like ICE automatics)
-- Apply brakes to simulate regen mode when necessary (battery 100% or too cold)
-- Apply brakes and blend out motor torque as car comes to a halt, release brakes when car is told to move
-- ...
By my reckoning, the throttle stack probably has 10x more lines of code than the steer stack. In fact, I'm pretty impressed by how smoothly the stack handles all the complexities of blending torque/regen and brakes into a near seamless throttle experience. There is a LOT of complexity going on that none or use are aware of (or need to be), but that doesnt mean it doesnt exist.