It's worth expanding that this is a very broad spectrum of software.
No one's worried about assembly code for Intel chips, but the next generation could be locked down.
No one's worried about writing C++ for Windows, but technically you're using their APIs and hooks that could be dropped in the next release.
There's iOS, where you're also subject to review and approval.
There's well-known web joints like Google, where this can happen.
Then there's the fly-by-night shops that could just dissolve tomorrow.
The safest thing is to build your own computer from silicon, write your own OS, your own compilers, your own languages, your own software, and your own APIs. Of course, by the time you do that, we'll all be dead. So it's a balancing act. But it's worth illustrating that you're taking for granted that things will remain the same forever, when in reality there's a sliding scale of risk.
Free software ameliorates this problem. The code is free to live on independent of its authors or parent organization. Sun may or may not have killed its business by making all of its software open and free, but the community benefited from that immensely when Oracle took over. We don't have to start from scratch, just have to use free software.
Your post also seems to assume that everyone will upgrade to the "next release". On platforms where you get to control your upgrade cycle, people won't upgrade if the upgrade breaks the programs they want to use, and this acts as a check on gratuitous API/ABI breakage.
Microsoft takes this extremely seriously and has hardly any API breakage over the last 20 years because they know that there's a real threat that a competitor could emerge with WINE pre-bundled and take away some market share if they break a lot of programs.
I think this shows when you should be particularly worried about vendor (supplier?) lock-in: if it would hurt you more than it would others, including the vendor.
My shareware Snood clone company is not very worried about Microsoft changing the Windows API, but I'm sure with every release major Windows software suppliers, particularly those reliant on a certain niche feature, certainly are.
No one's worried about assembly code for Intel chips, but the next generation could be locked down.
No one's worried about writing C++ for Windows, but technically you're using their APIs and hooks that could be dropped in the next release.
There's iOS, where you're also subject to review and approval.
There's well-known web joints like Google, where this can happen.
Then there's the fly-by-night shops that could just dissolve tomorrow.
The safest thing is to build your own computer from silicon, write your own OS, your own compilers, your own languages, your own software, and your own APIs. Of course, by the time you do that, we'll all be dead. So it's a balancing act. But it's worth illustrating that you're taking for granted that things will remain the same forever, when in reality there's a sliding scale of risk.