It was a damn meteor. Fossil recorde CV show a layer of dust within sedimentary rock around the world at the same exact period of extinction. From the same geniuses who believe in climate change, no doubt.
Only the meteor theory does not work as dinosaurs remained in the fossil record for millions of years after the meteor strike, same for the lava flow theory. So it had to be something else, which is the question.
It took millions of years for the dinos to die out, so it would have taken a quite remarkable timed-release meteor to do the job. A meteor impact, of course, might well have caused widespread kills and even extinctions at a particular point in time, which in turn could have significantly changed the dynamics for the survivors. Climate change might have figured in. Or new diseases.
I'm old enough to remember the rise of mammals being the conventional explanation. (Maybe it still is, despite all the talk about meteors.) The rise of mammals has the advantage of being a classic Darwinian explanation. Large egg-laying dinosaurs might have been quite vulnerable to smaller, quicker predators. The primary targets would have been the eggs and the hatchlings. How protective were dinosaurs of their nests and their young? Were they like birds? Or lizards? Or both, since birds and lizards are collateral branches of the family. Any beastie that didn't guard its young would be at risk to newly emerging predation, and the biggest creatures, being fewer in numbers, would have been the most vulnerable.