There is so much business software out there and ecosystems that have evolved around it. Systems still running cobol on IBM mainframes; or, more "modern" stacks like Java apps running in IBM websphere. There are relatively small numbers of HN reading folk that went to some of the best CS programs and/or work(ed) at FANG caliber companies (whatever you call them now). The rest of the software engineer types are a diverse crowd and turning to IBM Bob might be more natural than some creepy looking orange starfish offering. That's my hypothesis anyway.

That IBM Z skill locked behind an "enterprise only" pay point would be a good starting point.

I'm sure tons of companies have retainer spends with IBM for software, hardware, consulting, etc., and this is another way for their corporate clients to spend down / increase their retainers faster

See: Kiro by AWS