I think that kind of stance is partly intentional on IBM's part. Right now it's practically impossible to develop viruses/ransomware/etc. for any mainframe product, so mainframe owners get security equivalent to commodity air gapped servers, even when it's connected to the internet. Though behind firewalls of course.

Allowing hobbyists real software/firmware access will inevitably incentivize the creation of attacks since so much valuable financial data flows over mainframes, which everyone knows about.