Maybe all dinosaurs were wiped out, but birds (a reptiloid offshoot) flourished. And a lot of other reptiles survive to this day. Maybe the dinosaurs (many of which must have exploited similar ecological niches as fishes, birds, mammals, reptiles and amphibians) had some other vulnerability or weakness we are not aware of.

Not all dinosaurs were clumsy, over-specialized, high-maintenance behemoths, there must have been many small, adaptable and hardy species which could have made it. We know some (but not all) were egg-layers. They appear to have been very successful and widespread across many habitats, the most varied and dominant megafauna on the planet: the most common vertebrate of all. And yet, the relatively fragile frogs and salamanders survived easily, and dinosaurs did not.

Its almost as if some catastrophe hit today and wiped out all the insects, but the crustaceans, scorpions, mites and spiders survived.