This trivially becomes very fragile. Each of those 100 programs now doesn't just do stuff, but is held to a contract. A contract that it's well possible nobody

This trivially becomes very fragile. Each of those 100 programs now doesn't just do stuff, but is held to a contract. A contract that it's well possible nobody intended to provide, but yet organically happened anyway. And so you find that a small change somewhere like deprecating an option, fixing a typo, or adding extra data to the output makes the integration explode horribly in a confusing fashion. There's also that plain text is a horrible serialization mechanism. Every program has to deal with parsing text that's mostly made for human consumption and deal with things like imprecise boundaries and arbitrary limitations per tool and per system. Eg, /etc/passwd is a nice simple format, until you consider that somebody might want to use a ":" in a field, or to add more fields, or to store multiple lines of data. And all those quirks are specific for that particular file and may be handled subtly differently by other parts of the system. And internationalization is an extra bit of fun, which ensures random bizarre bugs that use ',' instead of '.' as the decimal separator, or just emit text in some language that isn't English.