that's not correct. libraries have versions for a reason. the only thing preventing the installation of multiple glibc versions is the package manager or the package versioning.
this makes building against an older version of glibc non-trivial, because there isn't a ready made package that you can just install. the workarounds take effort:
https://stackoverflow.com/questions/2856438/how-can-i-link-t...
the problem for companies developing on linux is that it is not trivial