The customer called because of what they saw in the kitchen at midnight. Six weeks later they haven't seen anything, which is exactly what they paid for and exactly what nobody knows how to write about.
So they type "great service" and post it. That review tells the next terrified homeowner nothing about whether you actually solved a German roach problem, whether the treatment was safe around a toddler, or whether the same technician comes back every quarter.
Whether you have 200 reviews or twelve, the problem is the same. Thin reviews don't describe the pest, the property, or the outcome, so they give future customers and Google less context than a review that names what stopped coming back.