My opinion on why this could now become a practical problem for people who still want to continue with React:

1) This will deter people and organizations from using such libraries. For example :- WordPress.com and many other companies have said that they will no longer use React.

2) Lower usage and application of such libraries means that lesser people will find bugs in them, lesser people will fork these libraries, lesser people will contribute to these libraries.

3) Facebook may itself lose interest in continuing to open source the library. Or add any new features to the open source version.

4) People may get stuck with bugs in such libraries and with no functionality being added to such libraries for years.