I don't think that anyone has ever 'decided' on that... we just don't have them and I don't believe we ever had. For a native speaker of Polish, it's having articles that is a strange idea.
I think a word like Duolingo should have all forms identical, but I cannot state it as a 'fact'.
That simplifies things – edited!
Is that perhaps a rule for company/trade names and perhaps some other proper nouns?
No, rather the endings. And -o ending is problematic: in theory it should undergo declension, but in so many examples it just sounds weird to Polish people...
For example, let's take Cristiano Ronaldo - until recently I had no idea that this name should undergo declension, I have never heard it or read it in any other form, but apparently it should be. For example "Cristiano Ronaldo's goal" should be "gol Cristiana Ronalda". But this looks as if his name was Cristian Ronald. I've only seen it once and it was an article on grammar.
(on the other thing, if we considered the real, Portuguese pronunciation, then both words end with -u and it is correct to not change them :D But how many football fans in Poland pronounce it correctly? Almost no one, I guess.)
These are just language-teaching sentences, they do not have to be true at all ;)
Just technically, but what's the point of learning and remembering false sentences, which you won't be using in real life? At least when I'm learning "just" is not of my satisfactory and where's an option to improve something, why desist?
Grammar. Also, having funny/weird sentences makes them easier to remember instead of just translating plain, boring sentences. And that's the point, that people should remember the grammar and be able to say what they want and not just repeat ready phrases. Those you can find in books known as "rozmówki" :)
Remember that the most famous phrase since this website was founded is "Yo soy un pingüino." - Duolingo even sells t-shirts with it ;)
I'm not buying it (rozmówki), and who does nowadays, in the computer age? And I don't want to remember false information. That's the whole point of learning, same when children do learn new language - they trust they learn true information about the world. The other side of the coin is that the education is actually a brainwashing system. But since we're all adults, I hope, we can distinguish false and truth, the rest is just pointless academic discussion. In real life nobody is speaking about grammar, but teachers.
You're saying on the one hand that you can differentiate falsehood from fiction, but on the other hand that it's problematic to have an untrue sentence whose only purpose is to teach you a grammar point. The point of this sentence is that it's teaching you things like negative sentences take the genitive, how to form the genitive plural. It's not attempting to teach you "the true facts about life", so I'm baffled why you're het up about it.
You know that some fish have teeth, but you should also now know how to make fish plural, how to conjugate "to have" in the third person plural, that a negative sentence takes the genitive, and how to put teeth into the genitive plural. Only maybe half of that would be true if it said that fish do have teeth.
(Also, "fish" is a pretty arbitrary term anyway, which has fairly shaky scientific boundaries as I understand it, it's not a very helpful term in biology, if you're going to get picky about it...)
The point of this course is to teach you the basics of Polish, not biology. I say, yay sentence.
Actually 'Fish have no lungs' is not a good example as there are many fish in the world with rudimentary lungs. The very fact that you are discussing this sentence so much proves that such sentences work and stick in your mind. :-) I like the more obscure sentences because they make you stop and think.
@flootzavut, No, it's not. The fact itself, that one is able to distinguish truth from falsehood, doesn't necessary mean, that one has to do it all the time. Especially when "learning", that idea implies getting and knowing the true facts about life, not about abstract grammar.
And if you would have read the whole discussion you would know, that "just" or "only" when it comes to learning is not of my satisfactory. I'm just raising the point, that learning should be about getting knowledge, ok? Leave the whole grammar spectrum aside. Get this: "Ryby nie mają płuc. - Fish have no lungs." is much better example. Period
I think having statenents that are not always true or sensicle makes it less likely my brain will unsramble the english tiles before i've translated the given sentence, so it works for me.