Ace on Base,
It’s up to the employer to set the mins they want, I used to love it when people would argue with me over the mins.
Their application never went any further.
Some operators like ATPL subjects for the following reasons:
Not being in a capital city, having to let employees go away for study
Not being in a capital city, having to let employees go away for exams
If you want to put an aircraft online that needs an ATPL holder as PIC, this person could be a co-pilot, and then move to the LHS when required without having to go away for exams/study
More knowledge
This list goes on ...
I have also heard of operators who say before you get you GR2 you will need to have 4 ATPL subjects, to get your GR1 all ATPL subjects.