Suitability is a protection, not a barrier
Enrolling somebody who cannot succeed has a foreseeable end.
Assessment of whether a student is suited to a course covers academic background, language proficiency and whether the course matches what they are trying to achieve. Where any of these is inadequate the likely outcome is failure, and failure here carries consequences that failure in a domestic enrolment does not.
The commercial pressure runs the other way, and it is strongest exactly where the risk is highest: at the margin, with a student who nearly meets the requirement, whose fee is already committed. That is the decision worth having a rule about rather than making case by case under pressure.
Language proficiency is the most common issue and the one most often handled by a form. A test score is a proxy, and where a provider has doubt, a conversation establishes more than a certificate. It also identifies students who would succeed with support, which is a better outcome than either admission without support or refusal.
Where a student is admitted with an identified risk, the honest response is to record it and put the support in place, not to admit and hope. The record also matters later, since a pattern of students admitted below requirement and subsequently failing is visible in the data.
It is worth noting that suitability assessment also protects the provider's other students. A class in which several students cannot follow the material changes the teaching for everybody, and the pressure to slow delivery or lower assessment standards follows from admission decisions made a term earlier by somebody in another department.