I've had this happen to me: a "no call no show" on other apps. I think sometimes people can't make it for various reasons and experience anxiety about it or embarrassment.
Maybe it's transportation, to childcare issues or maybe a spouse putting the Kibosh on a purchase.
Anxiety can be overwhelming and I think it accounts for a good percentage of the communication issues.
In any event it helps me feel empathy ( even if I'm incorrect: Lol)
It's because they can. There is no recourse for these very selfish people. You can't rate someone unless you sell something to them. They can do this over and over and over and no one else will ever know. The rating system on here is horrible.