Many of the bootcamps are relatively young with not that many attendees per year. Back-of-the-envelope calculation: ~50 per cohort, 6 cohorts per year is 300 students per year, times 3 or so years is around a thousand total enrollees. 100 reviews is 10% of people reviewing - that seems pretty high to me.

FWIW: I did a bootcamp, loved it, never wrote a review. Just laziness/generally don't write reviews for things. I would guess many people don't write reviews for the same reason.