I totally understand as I am having the exact same experience myself. I am not on IB but I do also accept first timers, as I think people have to start out somewhere.
My latest review was a 4*. I haven't had a 4* review in over 3 years, so it came as a bit of a shock but the written review was absolutely fine and like your guests they expressed their wish to return. I can only put this down as first timers not knowing/understanding the Airbnb review system. I did laugh when I got an email from Airbnb telling me that I got a 4 start review so there is obviously room for improvement !
What I have also noticed with a few recent reviews, is more people marking down in the individual categories, again all newbie guests. Some of these don't make any sense at all, 4* for accuracy, but with the added points of points of perfect description, matched the photos, all amenities supplied, so I don't know how that can be improved. 4* for cleanliness but says pristine kitchen, squeaky clean bathroom, spotless bed linen and furniture etc. I find it difficult knowing how the guests experience can improve to 5* when I don't know what the problem is !
But no, I don't have an answer to this apart from not accepting first time guests which really goes against what I believe in. I was a first time host at one point and guests gave me a chance to shine. It is very tricky because also I don't believe in speaking to guest about reviews beforehand, it makes me feel as if I am asking for a good review. I know some people put details about the review system in their welcome notes for when guests arrive, but again that makes me feel uncomfortable too.
I am waiting to see what this weekend brings. I have a guest arriving who is 5 5* reviews and another guest who is new to Airbnb. I have already had great communication from the reviewed guest, but no response as of yet from the newbie. Starting to make me feel on edge already !