Why did the dinosaurs became extinct

Because they died 65 million years ago and their bones was scattered all over the place.

The last dinosaurs died approximately 65 million years ago. Although the cause of their extinction is still a mystery, climatic change, diseases, changing plant communities, and geologic events could all have played a role.

Lately, dinosaur extinction theories have been the subject of much debate and controversy. A recent explanation, supported by many scientists, suggests that dinosaurs died out soon after a huge meteorite crashed to Earth near the Gulf of Mexico. A giant meteorite, they reason, could have landed with an impact that kicked up enough dust and debris to block out sunlight for a long time — leading to a deadly chain of events. Without the sun, all the plants died; without the plants, all the plant-eaters died; and without the plant-eaters, all the meat-eaters died. Sounds reasonable. But there is one problem with this theory: Paleontologists have not yet been able to find dinosaur skeletons in rocks dating to the period of impact. Some evidence even seems to indicate that all the dinosaurs had died before the meteorite hit.

What is the answer? As paleontologists search for clues to support their theories, they agree to disagree.

Where Did All The Dinos Go? Some Leading Theories

A big meteorite crashed into Earth, changing the climatic conditions so dramatically that dinosaurs could not survive.
Ash and gas spewing from volcanoes suffocated many of the dinosaurs.
Diseases wiped out entire populations of dinosaurs.
Food chain imbalances lead to the starvation of the dinosaurs.

You could solve them by trying something new that everyone can agree on or make a decision too.