Higher Education Institutions are autonomous with regard to their academic and administrative affairs, including in relation to admissions. Therefore any limits on the number of deferrals are a matter for the HEIs themselves and neither I nor my Department have a role in this matter.
I understand, based on the information available to me, that some HEIs are placing limits on the proportion of students in any given course that can defer a place until next year. This is to avoid a situation in which the number of places available to students applying in 2021 is significantly lessened due to deferrals. Students who are unable to defer their entry can re-apply to the CAO during the 2021 application cycle.