The V8 is the perfect ICE for the average size car. It fits sizewise, it has power without resorting to expensive addons (turbos, supercharger), and it's inexpensive to mass produce. The 8 cylinders firing in the V8 arrangement is quite smooth. V12's are nice, but have nearly 50% more parts. A V6 is OK, but not as smooth as the V8, and inlines or flat engines are never as smooth when the displacement is equal.

The current technology has given the engine super power, and long life, often exceeding 300K miles*.

In short, it is the right tool for the job.

*I currently own three and two of them are 300K plus miles and that is not unusual for the modern GM small block. The reliability and lifespan is legendary.