I think the crux of the issue is that there are many "abandoned" 32-bit apps that work very well and do not have good alternatives. I have grudgingly switched to inferior, but 64-bit alternatives for productivity and editing apps, and in the case of games or themed activity apps, had to let go or keep them in old devices.
I suppose the developers could be faulted, but even prominent companies like Disney and EA simply abandon old apps and it's really sad to see all those data created by me or my kids becoming inaccessible after the OS update. There are like, 8 Disney Princess-related activity apps I need some sort of exit strategy for.
On the point of "updating app doesn't make any money", there had been instances of releasing a separate app that users need to pay again, with the older version not working in a new version of iOS. Developer may take some criticism, but at least the willing customers will pay again if the app is good enough. But the thing is that much of the apps stuck in 32-bit land are basically in the "abandoned" category. The makers are no longer in the development world (bought out, bankrupt, lost interest, etc.) and even the big OS-level warning won't bring them back. There's no remedy but to put them in older, supported OS in order to use them.
Disclaimer: I'm one of such abandoned developer. Made several iOS apps a few years ago, but my interest had shifted and haven't gone back... not coming back, at least not in the near future. Sorry for everyone who used my apps.