A bit of public domain code can be used in a hidden way in perpetuity.
A bit of code covered by AGPL3 (for instance) (and other GPLs depending on context) can be used for free too, but with the extra requirement that users be given a copy of the code, and derivative works, upon request.
This is why the corps like MIT and similar and won't touch anything remotely like GPL (even LGPL which only covers derivative works of the library not the wider project). The MIT licence can be largely treated as public domain.
With the incentives set up like that, the era of open software cooperation would be ended rapidly.
People who understand and care about the implications of https://xkcd.com/2347/
Which admittedly is not nearly enough of us…