Search results yield coursereport.com and switchup.org.
With the "top" ones like GA, Hack Reactor, Career Foundry, you are lucky to get more than 50+ reviews.
With some of these being over $10k, am I wrong to think there should be more reviews out there?
a) simple laziness. A good review takes time and thought to write, and the time isn't necessarily in the writing the review, but in processing the experience after graduation. By the time you have a more balanced (ie, graduated, employed/unemployed) perspective, you've probably moved on to other things.
b) in my case, it's mostly due to general ambivalence about the experience. There were things I liked, things I thought weren't done well, and the overall effect is to cancel each other out. Ambivalence doesn't encourage taking the time (see above) to write down thoughts the way more extreme positive or negative views do.
c) also specific to me: I genuinely liked the instructors and most of my cohort, and writing anything negative seems impolite - not wanting to hurt someone's feelings or seem ungrateful. Irrational, but there ya go.