"Do you love me?"
This sentence is useless. First, it is too formal for a context that would never use the polite form. Second, a Japanese would never ask something like that. This example marks the difference between really learning a language and memorizing some sentences detached from reality.
Most of the sentences on Duolingo will not be used in real life by the students. As you say yourself, learning a language is not memorizing canned sentences and repeating them on demand, you have to be able to craft your own original sentences, sentences that you have never heard before.
So, we shouldn't mind learning a "useless" sentence just because we will never say it exactly as is, it is serving its purpose of getting us used to the language structure and vocabulary.
But it would be silly to never teach this only because IRL it's rare for people to use it: what if I want to understand songs or anime? It makes sense for us to learn it regardless, maybe they should just put an asterisk next to it to warn us it's usually "too strong to be used irl"