StackOverflow, I feel, inherently ties into the "Release early. Release often." philosophy: if you ship broken code , oh well , there'll be a release soon enough to fix it. This can not be borne in a mainframe environment. This is not to say there aren't bugs because of course there are but the expectation is completely different. This kind of "by your bootstraps" education is no bueno. You will get lots of training and excellent documentation. We used to measure the amount of documentation IBM ships with the mainframe not in pages but in yards it takes on the shelves.
StackOverflow in itself is the answer to the question "who you gonna call" -- because you might be alone, or you might be working on a small team where no one has better expertise, and usually you are working with open source and so no one is obligated to pick up the phone at the software "manufacturer". This scenario does not play in a mainframe environment: you are going to be part of a larger team, full of literal graybeards and when push comes to shove then you do have a contact number: your employer is paying absolutely ridiculous amounts of money to the software company and they will have a contact person who will pick up the phone.
StackOverflow in itself is the answer to the question "who you gonna call" -- because you might be alone, or you might be working on a small team where no one has better expertise, and usually you are working with open source and so no one is obligated to pick up the phone at the software "manufacturer". This scenario does not play in a mainframe environment: you are going to be part of a larger team, full of literal graybeards and when push comes to shove then you do have a contact number: your employer is paying absolutely ridiculous amounts of money to the software company and they will have a contact person who will pick up the phone.