One main difference is that pyo3 is safer and easier to use to build said modules and have them work correctly without issues. Thus modules which hadn’t been worth it before to build in this manner suddenly become so
There’s a whole legacy of wrapper interface generators like SWIG that are way more powerful than PyO3, QT is e.g. fully mapped to Python using a very powerful wrapper generator (SIP). PyO3 is just a really simple interface generator in comparison, look at what SWIG can do, or SIP, what PyO3 does is trivial in comparison.
There’s a whole legacy of wrapper interface generators like SWIG that are way more powerful than PyO3, QT is e.g. fully mapped to Python using a very powerful wrapper generator (SIP). PyO3 is just a really simple interface generator in comparison, look at what SWIG can do, or SIP, what PyO3 does is trivial in comparison.