My take is that they don't help and never have. Initially, people expected that the review snippet was a ranking signal. It proved that it wasn't, and I also doubt if people see the stars and click on the search results with five stars. Of course it attracts the eye but other than that, I believe only the titles and description can influence the click-through rate.
Reviews offered a helping hand to legitimate businesses and ended up abused and rigged. Trustpilot built a whole business around it, and it costs a lot of money to get in without any tangible benefit. For the rest, people started building fake star reviews (schema spam), and most reviews from real people are, in large part, incentivized. For all the above reasons, I'm sure Google will take them down sooner or later. I don't see any point a business should work hard on getting reviews. If the customers like to leave an honest review, they are free to visit the GMB page and leave it there for as good as it is. Don't sweat on getting reviews; it's not worth it.