It has to do with the challenge of evaluating systems like this. The only people who really can understand it are people who are actually implementing and using

It has to do with the challenge of evaluating systems like this. The only people who really can understand it are people who are actually implementing and using it at scale and its the nature of their experience that they can't write a review "... I work at company x and after millions of dollars I can honestly say that this product is piece of junk here's a bunch of complaints which dovetail into the heart of our company's business..." So we'll just have to live with the lone reviewer working in their home lab. "I created mailboxes for my cats and sent them 50 test messages without any hiccups, so Exchange 2019 looks like another winner!"