That's an interesting question. In the late 90s, IBM had a competition in the same S/390 architecture, with Fujitsu and Hitachi mainframes. These could compete with IBM on price, so I don't think this would be a problem. It's hard to discern cause and effect here - maybe mainframes are expensive because IBM held to them and eventually became a monopoly.

But I think the claims "mainframes are legacy and complicated" came sooner than that, and that was the real cause why people wanted to avoid them.

Compare this with Unix in the early 90s, it had a very same problem, being somewhat expensive and inaccessible, even for home PCs. But this changed with Linux... and in general, home PCs changed the expectation of the onboarding, before that, the fact that you cannot buy a computer at home, didn't present a significant obstacle in employee training.

I am almost wondering if any complex enough system is long-term commercially viable. Closed-sourcing somewhat inevitably means bleeding mindshare.

> That's an interesting question. In the late 90s, IBM had a competition in the same S/390 architecture, with Fujitsu and Hitachi mainframes. These could compete with IBM on price, so I don't think this would be a problem. It's hard to discern cause and effect here - maybe mainframes are expensive because IBM held to them and eventually became a monopoly.

I'm sure those were still really expensive though.

IIRC, IBM made a big investment to migrate to a 64-bit architecture, but none of its competitors in the mainframe space wanted to do the same.

> if any complex enough system is long-term commercially viable

I don't think you can determine this from first principles without taking the wider world into account. Things like the electricity grid or car manufacturing seem to have managed just fine over long periods of time, despite (almost) nobody having their own coal power plant or cylinder boring machinery. There are some niches in software that will survive just fine even as closed source software, SAP, Salesforce and industrial control systems spring to mind.

>electricity grid or car manufacturing

electricity grid became a commodity (I believe arguably car manufacturing did as well), not sure if the theory isn't that any system that lasts over the long term will either become commoditised or cease to be commercially viable.

Electricity feels like a commodity (although unlike the other commodity markets there's almost no "carry trade", nobody talks about contango power). The electric grid is a utility; on of those things that's either a state monopoly or a state-shielded private-ish company, because there can't be competing electric grids.

Grid equipment itself is manufactured by unglamourous heavy engineering firms like Siemens or ABB.

> Is that the main reason?

I think it is mostly the effect of them being legacy systems. Old systems become legacy systems if they are developed further. They can be difficult to work with but the mere fact that the language or platform breaks compatibility does not make that platform any better.

True, and maybe it's the same effect that drives ageism. Young things show promise and potential, while the old things are whatever they are, unsurprising, set in their ways.