Most tai chi chuan classes are not really teaching tai chi chuan.
They offer a health-only syllabus aimed at the non-martial student.
The combat curriculum (chuan) is missing.
Only a small fraction of the art is being taught. Over 90% of the material has been omitted.

In truth, such a class is teaching tai chi-style exercise.
It is not tai chi chuan.

Tai chi chuan is a martial art. A style of kung fu.
There is a world of difference between tai chi chuan and tai chi-style exercise.