Anyone with an older toolchain can’t build that library of anything that depends on it.
Some environments might not even have the newer version available.
Some environments might not even have the newer version available.
This may not get the project as many users, but not everyone who writes a 50 line project is trying to figure out which versions it supports and setting up full test matrices either.
If you have an older tool chain, it is on you to fix the library to build with the older tool chain, that's what open source is about!