The intake form is medical in everything but name. Births, surgery, blood pressure and symptoms are collected before anybody trains, and that information needs the protection of health data rather than the storage of a mailing list.
Improvement is slow and easy to doubt. Recording measurements at the start and repeating them at eight weeks is what shows a client something changed, and without that people stop before they see it.
Correction is the reason for small groups. The technique is done wrongly by almost everybody at first, so capacity is set by how many people one instructor can actually watch and adjust.
A referral deserves a reply. When a physiotherapist sends somebody, telling them what happened afterwards is what turns one referral into a standing relationship, and almost nobody does it.