I think one of the biggest factors, at least recently, is how long a review stays on the site's front page.The age of reviews definitely plays a role too, although that's really what I'm trying to say above. To add a little more data to back up your point, here are my own current stats:
- 225 courses played
- 16 states/1 country played
- 5 courses played in current DGCR top 10
- 223 reviews
- 3019 thumbs up/12 thumbs down
My stats are pretty similar to EspressoPatronum's, yet I am lagging even further behind in uniques at only 160. 160/223 = 0.72 uniques per review. Comparing my profile and EspressoPatronum's, we can guess at the reason why - his first review was in 2011 and although he didn't really become a regular reviewer until 2017, he does have 13 reviews posted between 2011-2014. In contrast, my first review was in 2020. It's very likely that most of those 22 extra uniques date from those 13 2011-2014 reviews.
Here are two reviews of mine. One is for New London Tech in VA (McBeth's course). I thought it was thorough and well written. It got bumped off the front page in less than a day. It has 9 votes in 9 months. New London Tech DGC - Reviews
My review for West End Baptist is currently on the front page. It was an updated review, originally from 2017. In the 3 days since my update, it's gotten 13 more votes due to its high visibilty.
One of these reviews took me 45-60 minutes to write. The other took 10. One I put effort into writing. The other, not so much. Yet, the lesser review has twice as many votes.