we eat soup in deep plates, not bowls.. so we say "тарелкa" cause it's a plate. but in english that sounds incorrect because people eat soup in bowls and not in deep plates. lol.. of course I can't speak for all american and russian soup eaters.. but that's how it is in my family.
"The simplest valid answer we can give - Russian is partially pro-drop. The actual degree of this "pro-dropness" is an open issue and a subject to debates."
One comment noted that Russian is partial "pro-drop" ("pronoun-drop"), that it is far less done in written Russian than conversational, but that it's acceptable where there is no ambiguity from the verb form.
Obviously, that requires context where verbs have nothing to do with gender (the conjugation table I use has Masculine/Feminine/Neuter forms for Past tense and Subjunctive, but I don't know yet how that works.) And, apparently, some verb forms are shared by different infinitives, so you'd need some greater knowledge in order to know whether your particular verb is ambiguous or not, so using the pronoun seems safer.
I accidentally dropped some subject pronouns (I'm studying Spanish and Italian, too) and was marked wrong, so it's not optional according to Duo, but that may be a mistake - or it might be real. Who knows.
For beginners in true Pro-drop languages, it's always safe to include pronouns in declaratory sentences, but in questions you easily can run into problems, because placement of the subject pronoun in a question can be dicey (problematic). Perhaps that's also the case with Russian - that it's easier to drop a subject-pronoun in a question than in a straight-forward declaratory sentence.
You cannot judge that something is incorrect baaed on Duolingo marking it as such.
Every correct amswer has to be added manually and even in simple sentences for simple languages you need dozens of accepted answers. Russian is very different from English with its conjugations and declensions resulting in even more needed answers.
Ultimately this means dozens to hundreds of answers per exercise are marked wrong by Duo despite being correct. Its just a lot of work and addition and is made even worse by the fact that people often donr report the errors or they post about them in the forum instead of reporting them so they are not seen by controbuters.
It's only applied to the bowl because the bowl is what we're talking about. The soup being in genitive is just describing the bowl. If we had an adjective describing the bowl then the adjective would take the same case as the noun, but here we just have two nouns, the one we're talking about takes the case the verb takes (accusative here) and the one in genitive just stays in genitive. I wonder if that makes any sense.
Хочешь синюю тарелку? Я люблю мою чашку чая.
Could be so (I think it is). But not forgetting, most times the Genitive Case is "...of ...", as in the sentence "A bowl of soup". (Genitive - possesion, quantity and negation)
Plus, there was this sentence too "Хочешь супа?" and it was translated as "Do you want some soup".
I'm not native and not very advanced, so these might not be exactly correct, but close enough to give you an idea.
A plate of soup = Тарелка супа (супа is in the genitive, aka second case тарелка чего? Супа = A plate of what? Of soup)
A soup plate = суповая тарелка (basically have to use an adjective here, and russians would probably never say this. Better translation would be глубокая тарелка, a deep plate)
A plate for soup = тарелка для супа (супа again is the genitive)
Finally, the translation to do you want a soup bowl/plate ? is "Хочешь глобокую тарелку?"
This is a feature of the Russian language. Consider this an established expression. People eat from a plate. The cat drinks milk from a bowl. The dog is eating from a bowl. The "bowl" is also used for cooking. You can put some semi-finished products in the bowl. You can put popcorn in a bowl and eat it from the bowl when sitting in a chair in front of the TV. There may be a bowl of fruit on the table. But people always eat from a plate. Soup - from a deep plate, main dishes - from a non-deep plate. Pets eat from bowls.
I'm sorry, my English is not very good. I hope this is an understandable explanation.