You might as well ask, "If we came from fish, why have fish stopped evolving?"
Nothing still alive has stopped evolving.
"And it raises questions about why monkeys, which are supposedly evolved from the same branch of the tree, stopped evolving..in fact, stopped evolving for millions of years."
They haven't stopped evolving.
Actually, they haven't. They've been evolving all this time, too. You won't find many, if any, modern monkey species that go back several million years.
Good.
"It suggests that since we all exist in the same plane of time, we are all equally evolved. We just evolved to different things, but the level of evolution is equal.
Why is that the logical outcome? Evolution is constantly happening, at varying speeds. There is no level of evolution. There is no direction to evolution. There is no purpose inherent in evolution. Evolution is simply the outcome of allele variation and various types of selection.
"It raises questions about Budhism... maybe we should not kill a bug because it is equal in evolution to us?
Again, why do you feel a bug is equal in evolution to anything else? Apart from any moral decision you might want to make about killing specific organisms, you need to understand the continuity of evolutionary change at quasi-random rates in a population of organisms. There is no method of quantifying the relative distances that organisms are along their respective evolutionary paths and assigning some qualitative value to that point.
"And it raises questions about why monkeys, which are supposedly evolved from the same branch of the tree, stopped evolving..in fact, stopped evolving for millions of years.
Where do you get your ideas? Monkeys have not stopped evolving. Each species evolves at a different rate than other species, even related species, depending on a large number of factors.
"Has anyone found the equivalent of an Australo-pithecus for the chimpanzee?