Telemetry for me is table stakes. We have been doing forms of tracing (first home grown) since 2012. Strictly speaking only the edge gateway needs to know about it.
Tracing is trivial to add with OTel. It is trivial with Spring Boot (since v3). At least on technical endpoint level. Adding tracing to business logic obviously requires work, but simple propagation is table stakes.
you really only need it at the entry point to have a trace ID... but yeah. tracing is hard to add on later, though I'm glad it's becoming more common for newer code.
It's like you get to the middle of a recipe and they say to "just" add in the meat you've already been marinating for 48 hours.