Because obviously we understand that they are in a business, they cant keep on producing vaccines when they know that the demand for vaccines is very low. 
Nekuti tinonzwisisawo kuti vanhu ava vari mubhindauko rekuitawo mari, naizvozvo havagone kungoramba vachigadzira mishonga iyi  asi vachiziva kuti vanoda kuishandisa vashoma.