The relicense had nothing to do with that and it wouldn't stop RetroArch regardless. They ship RA with several by-license-text incompatible[0] emulators anyway; many of their cores are under non-commercial licenses and some are explicitly included against the wishes of their original developers; ask the MAME devs what they think of RetroArch.
Stenzek changed the license because he had a meltdown last month when PCSX2 changed it's license from the LGPL to the GPL (which is allowed by the LGPL; there's nothing dubious about making this change)[1] for... some reason. In response, he threw a tantrum and closed all his open PCSX2 PRs, effectively quitting the project[2][3][4].
RetroArch is a plague on the emulation community, but that's not why Stenzek relicensed his emulator.
[0]: If this is actually incompatible will largely depend on your views how the GPL interacts with dynamic linking. Don't just repeat the FSF FAQ, look for other legal opinions not written by free software advocates.
[1]: https://github.com/PCSX2/pcsx2/pull/11648
[2]: https://github.com/PCSX2/pcsx2/pull/11315
[3]: https://github.com/PCSX2/pcsx2/pull/11401
[4]: https://github.com/PCSX2/pcsx2/pull/11449
Stenzek changed the license because he had a meltdown last month when PCSX2 changed it's license from the LGPL to the GPL (which is allowed by the LGPL; there's nothing dubious about making this change)[1] for... some reason. In response, he threw a tantrum and closed all his open PCSX2 PRs, effectively quitting the project[2][3][4].
RetroArch is a plague on the emulation community, but that's not why Stenzek relicensed his emulator.
[0]: If this is actually incompatible will largely depend on your views how the GPL interacts with dynamic linking. Don't just repeat the FSF FAQ, look for other legal opinions not written by free software advocates.
[1]: https://github.com/PCSX2/pcsx2/pull/11648
[2]: https://github.com/PCSX2/pcsx2/pull/11315
[3]: https://github.com/PCSX2/pcsx2/pull/11401
[4]: https://github.com/PCSX2/pcsx2/pull/11449