I've been turned down by several people for reasons like that. Complaining about it doesn't help; you can't control what they do; you can only control what you do.
If this situation happens where they cancel for some reason, I would text them "All good, no worries. Let me know when you're up to it and we can meet another time.". Then, just leave the ball in their court. If they message you back and try to reschedule, great. If not, then don't message them again.
If they don't want to go on a date, that's totally fine. Why would I even want to date someone that doesn't even want me? When I can focus on finding other people that do want to go out.
