What incentives have professors to teach a large class (vs. a small class)? I am wondering about what incentives professors have to teach a large class (vs. a small class). To put it differently, when a professor is assigned to a class, what motivates him/her to attract students to his class? I am looking for external motivations, not personal ones, such as willingness to share the class materials to as many people as possible.

I am mostly interested in the United States, but curious about other academic systems as well (at Mars University there seems to be none).
At my institution in my department, I think there are two major external incentives:


The number of teaching assistants is a function of the number of students in the class. Critically, below some threshold size n, a professor will not receive any teaching assistants.  
Offering the class in the future may depend on enrollment in the present.


In some other departments,


Professors who teach classes with more than N students get double credit for that class, so if they typically teach 4 courses a year, they could instead teach 2 small courses and one large course with >N students.