There are many reasons guests don't leave reviews. I'd say on average 1 in 3 guests leave reviews. You could send them a gentle email asking if they would leave a review if they enjoyed their stay at your place. Also check if the guests also wrote a review and you are the one who needs to write a review for the guests review to be visible. Otherwise if you don't write a review, then a guest's review is only visible after 14 days.
How many bookings have you had? It's not unusual for 25%-50% of guests to skip the review.
Try temporarily reducing your rate by maybe 25%. That might sound extreme, but you'll a) get more bookings and b) probably have some happy guests, who will give you happy reviews. After a few positive reviews, adjust your rates back up to where you really want them.
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