I don't really see where the therapist has a big obligation here. Sure a reply would be nice, but unless you requested one, the ball is in your court to set up another appointment

No shows and late cancellations are not uncommon in medicine and therapy. It would bog down the practice to follow up on every one of these, unless there was a concern for said patient's health.

Plenty of paperwork to catch up on in those extra 50 minutes