If I’m descended from Europeans, why are there still Europeans?
A lot of life is slime.
I’m descended from monkeys. My mother is a monkey, as was my father. For that matter, I’m also three monkeys’ uncle.
One could, of course, be more specific. All of the monkeys in question are Old World monkeys. If one wishes to be more specific yet, they’re all apes. And for a very great degree of specificity, one might say that they’re all from the single most numerous species of ape, Homo sapiens. But they’re still all monkeys.
Unless you live in a pineapple under the sea. 
And why is there still clay?
Okay, try convincing Victorians and Young Earthers of that then. 
Two monkeys lived in a cage at the zoo. One of them just finished reading Darwin’s Origin of the Species, which he then attempted to describe to his cage-mate.
The other monkey, incredulous, asked: “You mean to say that I’m my keeper’s brother?”
Probably a misremembrance of a scene from* Inherit the Wind*:
Happy birthday to you
Happy birthday to you
You look like a monkey
And you’re descended from one, too!
Love Inherit the Wind. I was very disappointed to learn that the original trial was little more than a publicity stunt.
“If God made Adam from dust, why is there still dust?”
“If God made Eve from Adam, why are there still men?”
Why do I still have all my ribs?
You started with the baked beans?
If Americans came over from Europe, why are there still Europeans?
I think they doth protest too much.
No doubt. But a little of my youthful innocence was lost when I found out it wasn’t a crusade against ignorance. Instead all the parties involved sat down and decided to have a circus.
No, it wasn’t. I’ve discussed that more fully here, especially in post #12.
Other than involving evolution the trial bore little resemblance to Inherit the Wind, which is a very fictionalized work of fiction.
There’s also an idea in many branches of Abrahamic religions that Adam and Eve were the most perfect humans and each subsequent generation is more corrupt and farther from their god’s ideal. That’s why, they’ll point out, the earliest people mentioned in the bible lived thousands of years and we only live to be a fraction of that. To them it actually seems like a logical argument to say “If monkeys were our ancestors we’d be less intelligent than them and live shorter lives. Instead we’re more intelligent and longer lived so we can’t be descended from them. Even a scientist can understand that.”
Nothing you said there or here contradicts what I said. I’m not sure if that’s what you meant. Each side had their own agenda. All involved agreed to have a trial for their mutual benefit even though their benefits were different from each other. And you are correct it was much different than the play.