Why do some professors not recommend any text books for a course? I took a semester where a professor was teaching Statistics. He gave out no lecture materials nor the name of any text books.

When I asked him for a text book name, he gave me a name of a 900+ pages' book.
I could not find anything relevant in the text book which matches his lectures.
Finally, I quit the course.

The same thing happened whilst undertaking my Numerical Analysis course.

See this YouTube video named Introduction to Computer Graphics at 16:31. This is okay may be for 3D computer graphics. But, I guess, not good for math.

Why don't some professors recommend a text book for a course?
Reasons why I do not use textbooks: 


Most textbooks in my experience are bad. 
Most students do not read them (probably because they are bad). 
They are expensive. 
They do not align with how I want to teach the course.
I can provide the relevant subset of content myself.


I can't see a reason to use a textbook in my courses other than for supplemental material (even then, I would much rather point them to some free PDFs/slides from various faculty that are online).