High reliability/availability, data integrity, and the insane IO are the main pros I can think of. While there is a lot to talk about there, I think all of tho

High reliability/availability, data integrity, and the insane IO are the main pros I can think of. While there is a lot to talk about there, I think all of those points are dwarfed by the main draw: legacy support. Companies running mainframes typically have decades worth of code that is running on the mainframes and the cost/risk of migrating is enormous for questionable gains. I definitely agree accessibility is an issue. I am pretty young myself and found COBOL to be pretty easy to learn and start developing production applications with, in many ways easier than modern systems due to lower complexity for the dev. However, the systems side of things felt very alien to me and has been a challenge to learn. I don't know how one could learn it without training at a company that has a mainframe or by taking courses with IBM.