Thanks for posting. It is a good question that rarely gets asked.
Work experience plays into 3 things:
1. Admissions (duh, obviously)
2. Contribution to the school diversity (e.g. you were a caddy to Tiger Woods or PA to Steve Jobs or athlete or military or something unique such as a prolific DJ)
3. Recruiting
It is best to start from the #3. If you have a weak work experience, recruiting will be challenging. You will be competing with a ton of your classmates and a ton of other mba grads and the only differentiation you will have is your WE. Right? With weak WE (it is possible to mitigage it with a good brand - e.g. Amazon, Coca cola, 3M, Boeing, etc). Anyway, with weak WE, you will struggle.
That makes you unattractive to schools. They want to look at your resume and see someone who will be hired right away. That makes them look good - it is always better to bet on winners. Makes the program look good, makes their salary figures good and recruiting stats great. So the school is less likely to admit you, as the result of you looking less attractive to recruiters.
As to #2, your contribution to class discussion - that's debatable. Potentially you are adding diveristy but I am not sure this is the type they are looking for. Usually schools are looking for a growth trajectory, unless there are reasons why you did not have any. It is not about what you have achieved vs. othes but what you have done with the resources you have had avaialble to you. If you grew up poor, your performance is evaluated difference than if you have attended a private prep school and never faced adversity.
Hope this helps.
BB.