All agreed, but no matter how you shake it, it is tricky.
Sure, a large % of the universe just buys everything from Siemens (particularly countries which got a lot of money from the EU; it seems to be one of the conditions of the loan, along with Thyssen-Krupp etc) but this only pushes the project archiving challenge out a bit – because Siemens will never give you sources etc. And I know from 30 years of doing custom protocol converters that even in a firm of that size, the people who knew about it will be gone 10 years from now, and probably much sooner (most really smart engineers are within 10 years of retirement 
). Even if they have the sources (they usually get them because they pay for the job on a daily rate) they simply lose them. Then what do you do about the compiler etc? Best way is to set up a VMWARE VM and archive that; all 10GB of it. I know a firm which “archived” the whole PC, but a PC will probably not start after 10-20 years (hard disk seized up, crappy chinese PSU electrolytics dried out…). You need a massively disciplined organisation to keep track of some custom box they supplied 10-20-30 years ago. IME, even the biggest firms like [insert the biggest industrial automation name you can think of] will lose the stuff 1-2 years later.
I have a customer in Norway who buys our boxes for £200 and sells them for £3000, to cover long term support costs. This, of course, has never materialised, and everybody there will be retired or dead before I pack up writing code 
This allows them to chuck the £2800 at, say, Siemens, one day.
Your comment about fashion is why most older coders get to hate the job when they get past about 40. Every year you get another bloody fashion. In the server-side game, some of it is driven by genuine security issues (hacking never stops and you can only ever be behind, never ahead, the chinese and the russians) but most is just fashion. So they move into management The ones who continue to love it are ones running their own businesses, like me.
According to the internet your phone was done in C. Apple IOS, no idea.
Java? Fashionable? I don’t think so. It’s been around since the 90s and is firmly in the “boring, but lots of people know it, does the job well, has a mature ecosystem, and very widely used” category.
Perhaps Java was fashionable in 1997.
Java is good for server-side stuff because there it runs on the same system all the time.
It is bad for client-side stuff (both browser client, and PC executables) due to compatibility issues. Look at the AFPEX tool… Probably because it isn’t often used for that. IMHO anybody doing client-side or standalone apps in Java is being “rather fashionable”. And probably doing that is rather good for job protection, which would definitely have been the #1 guiding objective among the NATS coders or their subcontractors
