There are, in fact, a lot of 32-bit ARM chips still being deployed today. Yes, arm64 is usable, but using e.g. a Beagleboard- or even Raspberry Pi-class device still often makes sense (for cost or compatibility reasons.)
Those 70s and 80s programmers were working on mainframes with multi-decade depreciation. We work on servers and projects with 3-5 year deprecation when we aren't working on evergreen cloud configurations. Not to mention we've already standardized on 64-bit systems, outside of mobile, which is soon following and has typically a 2 year depreciation anyway.
Airline reservation systems run on software written in the 50s and 60s
Your views on evergreen this and disposable up to date that are very naive.
Embedded systems and business systems live for a VERY long time.
But some industrial- or military-spec ARMv7 core running a critical embedded system or two, in 2038? Twenty-year design lifespans (often with servicing and minor design updates) are definitely not unheard of, and successful systems often outlive their design lifespan.