@Alison754 I set up my Airbnb account in 2016, but only started using it this year when I began hosting, and have also had quite a few guests with no reviews but old accounts, so I don’t think it’s uncommon. I think it’s because Airbnb prompts you to set up an account quite early in the process, even if you’re just having a bit of a browse. Most guests that I have hosted don’t have any kind of profile description, unless they’re hosts themselves.
At least with an older account you know that it’s less likely to be a guest that had bad reviews, who had to ditch their account and set up a new one! Also, not all hosts leave reviews.
I have my IB to the same settings as you, so if I get a request to book and the person has no reviews, their opening message can go some way to telling me what kind of guest they will be. If they write a polite, thoughtful message, telling you about themselves and why they’re coming to the area and how much they’re looking forward to spending time in your beautiful place, then you’ll probably have a polite, thoughtful guest. If on the other hand I get a message such as one I got the other day “Holiday and after lunch cheers!” (my check in time is 2pm) then that’s going to make me pause (and, in this case, decline).