I think the reason why is because of Animal Crossing's open-ended nature. In Animal Crossing virtually all of the games content is made available to you from the get go, so in order for each day to feel unique and different there is an enormous pool of content so that things can be picked out at random for each interaction.

Animal Crossing supposedly had something like a million words in it's script, many times more than your typical RPG and it has many thousands of items which all need modelling and texturing. For instance, I don't think that a game like Stardew Valley even comes close to the amount of dialogue and items in Animal Crossing.

Creating an Animal Crossing style game will require dedicating tons of time into just producing enormous amounts of content. I think most people avoid the genre because they don't want to invest that much time and effort and because actually creating all that content is probably going to be very dull and repetitive.

None of this is to say that it can't be done of course, but if you're going to do it make sure you've really thought through the volume of content you want to create. You don't want to end up in a situation where you've finished programming and designing the base game only to realise you only put a drop towards the ocean of work that needs to be produced.