I think what people are missing is that sure, code "rots", at the very least because of security patches. But since this all happens to everything simultaneously, the more distinct layers and support tools you have in your stack, the more often you have to deal with
something breaking in a nontrivial way.
In short: the more moving parts you have, the less time you have between major malfunctions.
(Manufacturing and hardware world understands it well, which is a big part in why they like integrating things so much.)
So e.g. over in the backend-land where I live, it used to be that I had to occasionally update the compiler or one of the few third-party dependencies that I used. Today, I have many more libraries (to the point there's something to update for security reasons roughly once a month, on average), and on top of that, I have CI/CD introducing its own mess, Conan updates which occasionally get messed up, or make some existing recipes incompatible, CMake updates which are done unexpectedly and break stuff, now also Docker is adding more of its own problems, etc. So I have to deal with some kind of tooling breakage every other week now.
And always, always, when I think it's all finally OK and I can get on with my actual job, some forgotten or hidden component craps itself out of the blue. Like that time our git precommit hooks broke for me, because someone changed them in a way that doesn't work with my setup. And then me wasting a day on trying to fix it, eventually giving up and degrading my setup to unblock myself. Or another day where, for no apparent reason, some automation that made automated commits to some git repos started losing Change-ID headers in commit messages, making Gerrit very sad, leading to several people wasting a total of several person-days trying to fix it. Etc.
There's always something breaking, the frequency of such breakages seems to be increasing, and it's a major source of frustration for me in this job. Which is why I too am often thinking back to "good old days", and am increasingly in favor of keeping the amount of dependencies - both libraries and tooling - to a minimum.