Why was the model T automobile so popular?

Because it was a car the average American could actually afford. In 1908 when the Model T came out, autos were only owned by the rich as they were hand built and very expensive to own and maintain. The Model T on the other hand was relatively cheap, and was easy to maintain. It cost around $850 which is equal to around $20,000 in todays money. Other cars cost 3 or 4 times as much. It got cheaper and cheaper until 1926 when it was selling for $250.