Your point being? The horses were replaced alright, carriage drivers are thriving ever since.
I, in turn, suggest looking out of the window: modern carriage drivers are called truck drivers and their number is edging towards 10M worldwide.
Now add to this rail carriage drivers, sea carriage drivers and air carriage drivers. Years of progress changed the way you feed your "horse" and made reins somewhat more complex, but fundamentally nothing changed.
No employment stability, no benefits, no health insurance, no vacations, at complete mercy of basically a single company.
Yeah, thriving.