I believe Chrome speech synthesis is network-based, there is a noticeable delay while it downloads the audio and it won't work if you are offline.
NWJS uses the default speech synthesis service built in the OS and it works offline.
I guess that explains why everything I made it say took 2 or 3 seconds to start haha. I was OK with that, but yeah. I just wish speech synthesis could be more of a per-app thing like if I include voices with my game then the OS would be able to use them without the user having to bother installing them all so they get the same voices I intended.
Ultimately not a big deal because the option was just to make the game silly on purpose.