USCIS as a whole is well aware of its flaws. There plenty of publicly available reports and audits that describe in full detail where the problems are and how could they improve.
We can safely conclude based on the increasing waiting times, that those issues have not being fixed.
Take in account that USCIS is a mix of employees, contractors and software that are not always in direct communication.
You just said it yourself: "the unlucky ones". Being processed faster, your case being placed with an efficient officer, are all a matter of luck.