I think the main goal is to show you that while they are incorrect for the context that they are looking for, they’re still correct and just wouldn’t fit in as well. I think that especially in the early stages of learning, it helps to reinforce the different levels of formality that are inherit in Japanese speech, and that sometimes you can mix up the formality, for better or for worse.
I personally grew to like this, as it helped me to better understand the nuances as I was learning things more.
I’ll also add, that over time, these types of answers start coming up less frequently, and they’re more direct about the politeness level they’re looking for and whether you got it right.
As for auto-expand info only showing up when you get an answer correct, I think there is some intention behind that. I’m still working on N5, so I’m not exactly deep into this journey, but in my very early stages, I would immediately show the answer if I didn’t feel like I was totally confident in my guess. What I’ve found over time is that it’s more helpful if I try to guess a couple of times before giving up and looking up the answer, and I think that’s the intention behind this behavior. I believe that the goal is to get you to try to recall the answer on your own an donly then should you look it up. In the early stages, you’ll be looking them up frequently, but as you go, you’ll get more confident with guessing, and more OK with guessing wrong and having the item come up more often.
Just this morning I was doing a vocab review and I knew that I knew the item and had guessed it wrong a couple of times, but couldn’t recall right away. So I got up and thought about it while I did a couple of chores, and after a minute or so of thinking through similar-looking items, I remembered, and it was a great feeling! I think that kind of thing is what they’re after with that behavior.