When customers are standing by willing, able, and already paying a premium for every bit of speed that can be delivered, with no end in sight.
And you want to get in the door of an already-occurring cash flow without having to create your own new market.
A faster horse than they've ever seen will get their attention immediately and make you money right away.
Even if you've already invented a Model T, have a working prototype, and are highly aware of the promise of mass production.
Once you're actually prevailing in the market for speed itself, then you have the best position to leverage the imagination about the possibilities of a world having automotive garages, pavement, motor fuels, etc, and your little invention delivering the no-end-in-sight that horses will not be able to keep up with.
This is a way of funding growth by directly participating in the target market you are planning to disrupt.
An established market is at least somewhat rational compared to a not-yet-established market, but at least it's already a market.
There were others long forgotten besides Ford who launched with cars trying to survive when there was only a horse market, they all became unknown because they failed to remain solvent while the new market was still becoming existent, then rational. Ford is a survivor head and shoulders above the turbulent waters.
Some established coach makers prospered with the arrival of the automotive age (simply supplying the faster buggys the motor companies needed for their mechanical horsepower) while things like highly innovative EV's never got past the prototype stage or off the drawing board.
Ford succeeded in creating a new mass market for his particular invention, which only allowed participation by others having products of great similarity, but could not keep them out within IP limitations.
He had a low cost advantage that lasted years also.
A very bold vision to insure worthwhile copies of his invention were available, and if popularized, many copies, each adding value to raw materials beyond the financial gains attainable.
Him and Edison seem to have a lot in common and enjoyed spending some time together real well.
He must have gotten a hold of more resources to work with compared to your average used horse salesman too.
Not every problem needs a scalable solution, and bandaid is perfectly good. But many problems do need that.
So, start with the problem and go from there.