Why don't Dinosaurs exist anymore?

Dinosaurs have become extinct probably due to following reasons

1- Large meteorite impact that was the size of nearly one forth the moon.

2- Catastrophes like large scale volcanism and earthquake, followed by release of huge amount of co2 and other gases in the atmosphere which led to blocking of the sunlight.

As a result the global temperature dropped and certainly the reptiles(dinosaur) could not efficiently adjust to it due to lack of food, proper oxygen and water.

Hence the planet witnessed a major paleoclimatic change.