Are you certain? Japanese is like any other language, and has regional accents. I seem to recall my sibling's Japanese professor (a native of Japan herself) explain that whether a person audibly pronounces the U in words like suki or not, that it reflects where they were raised.
If you ever run into a bug like that make sure to take a screen shot and send it in a bug report with as much info as possible: https://support.duolingo.com/hc/en-us/requests/new
好き is the nominalized form of the (now obsolete) verb 好く
Similarly 嫌い "dislike/hate" is the nominalized form of the verb 嫌う
It's not really clear why there was a shift from the verb to the adjective in modern usage. Theories include that the verb forms mainly refer to the transition of state from not liking to liking (or not disliking to disliking) and the adjective/noun form for the state of liking, and that using a verb to state like/dislike felt too direct. Japanese is a very indirect and polite language so using the nominalized form to describe something as "is liked" rather than the more pointed transitive action of "I like X" is softer sounding.
There is a verb with a similar meaning still in modern usage though: 好む・このむ meaning "to prefer" (whose polite nominalized form is お好み ・おこのみ meaning "choice, preference". If you are familiar with popular Japanese street foods you may recognize this from the dish お好み焼き okonomiyaki, lit. "cooked as you like it")
Duolingo teaches through trial and error: the most positive way to learn anything. And after you errored out you were shown the correct answer, right? And now you know it, correct? You are on to it and have mastered it now, that not so? If so, then what are you crying about?