Why did ford stop building the model t?

The Model T had become out of date. When it was built in 1908 there were very few paved roads in the U.S. and most were either dirt or gravel. The Model T fit those type roads well with it's high ground clearance and rugged build. It would go just about anywhere. Times changed and roads were paved. People wanted a better riding car that was much faster than the Model Ts top speed of around 40-45 mph and it's measly 20 H.P. It was built from 1908 until 1927 and was basically the very same car except for minor changes. No model has lasted any longer than the Model Ts 19 year run with almost no changes. Ford came out with the Model A which was a great improvement over the Model T. It was faster, had more power, road better, and was a vast improvement.