Once systems acquire sufficient technical debt, it's packaged up into maintenance contracts and sold to offshore development companies to support.

Treating one part as the 'product' and other as 'waste' is merely a matter of perspective.

Eg in the early days of web search, think Yahoo and friends before Google showed up, someone might have shown you a banner ad, but most of what is now used as essential data to target the ads better was just 'data waste' that only showed up in server logs at most.

The waste is uncaptured value. It is some part of your software business's domain that is just too hard, expensive, or requiring physical intervention to encode the process in their system. So the business never chooses to build that feature. This leaves some part of your business's problem domain unsolved. Potentially someone else smaller could come in and try and solve that problem and capitalize on that wasted value.

Start ups that could have been viable small/medium business but were scaled to death?

It has several flavors, but there are some common themes and causes. Developers simply like writing code more than they like writing documentation, and they like writing documentation more than they like maintaining old codebases. Meanwhile, software vendors of all kinds have universally decided that they shouldn't be spending any money on any form of technical support that comes with a heartbeat.

Down in the home and small-business markets, there are a lot of people that get absolutely screwed by this. New software comes out, something tries to auto-update (or the user is forced to update), something goes sideways, and ... that's it. Stuck. Nobody to call. Some really sharp Google skills once upon a time could sometimes find an answer, but even that's thoroughly rotted out now.

So if your small business has your entire customer database in an old version of Quickbooks running on the office PC with Windows 7 configured by the last tech to stop complaining about updates, and then one day Quickbooks refuses to launch and displays instead an obtuse error message ... what do you do? For a while, you could call me, and for several years, I mostly enjoyed building a business out of fixing these sorts of things (and helping people navigate the sometimes very tricky update process so that this wouldn't be a recurring problem).

Unfortunately, software kept getting worse, documentation kept getting harder to come by, Google kept getting worse, everything kept getting converted into subscription SaaS (which meant that most of my answers started becoming, "yeah, that's just how it works now, I can't do anything about it, yeah, it sucks, yeah, lots of other people are complaining too, no, there's nobody you can call, sorry"), and I never felt good charging a lot of money for getting people out of bad spots.

I eventually noped out of this in favor of relaxing for a while in a slightly less hopeless part of the industry, but there's still a huge, under-served market of people who are getting hosed by sociopathic technology and would pay someone just to make it work again.