TimeZoneSidKey field in user object not returning entire list of picklist values in when executed in apex context but its working with workbench

Question

code used in method to fetch all the timezone value list:

List<DropdownWrapper> timezones = new List<DropdownWrapper>();
Schema.DescribeFieldResult descField = User.TimeZoneSidKey.getDescribe();
List<Schema.PicklistEntry> pickValues = descField.getPicklistValues();
        for(Schema.PicklistEntry f:pickValues){
           timezones.add(new DropdownWrapper(f.label, f.label));
}
public class DropdownWrapper{
        @AuraEnabled public String label { get; set;}
        @AuraEnabled public String value { get; set;}  
        public DropdownWrapper(String val, String labl){
            label = labl;
            value = val;
        }
       
    }

Above code is only returning 99 timezone values. But when checked in user setting its showing 400+ timezone values. How can i get all timezone values provided in the user settings in apex class. Above piece of code is returning 429 record in workbench and anonymous window but while executing in apex context its only returning 99 values.