Why are the dinosaurs pointles?

To answer to this question will be simple, but I want to make you understand some of the term I'll use to say the answer, so first of all:

• THEY are not marker fossils, you will ask why, well to answer to that I will say what a marker fossil is, and it is a fossil that appear in a wide range of place and can be found easy on the terrain and most important it gives you the relative time and space when the rock in which was found has formed, OK you will say that the dinosaur didn't appeared from the beginning of the earth, true but still they had a life spawn as a species to great to be good markers.
• THEY are not great environment indicators, a great environment indicator is a fossil that can show you what changes happened and make it adapt to the new condition, either by speciation or by adding new traits, you will tell me that this is the case of dinosaurs, but no, actually they hadn't changed so much to make them a different species or give them a trait that can define them as good environmental markers

Well this are the main types of index fossils and dinosaurs are'n included in then the situation is approximatively the same for all the vertebrates or chordates, the only differences are some species of fishes and some early reptiles, as so as some early types of chordates.
So you will say that "OK so dinosaur and couple of other vertebrates are not good index fossils, but they are good at something though right?" unfortunately no, they leave great track fossils, and other type of fossils but this will only help you if you are a geologist and need to see the top of the bottom of a rock layer or if you are a evolution biologist and may show you the transformation that occur in the transition of species but no good for palaeontology because most of the palaeontologists study the formation of the time and because palaeontology is just a tool to correctly define some geological problems as oil traps or the extent of geological time.
And they are not a good building fossil to, the best fossils that are of this type are the molluscs and corals and in some case the sponges