Even where it works, speakers are much worse microphones that dedicated microphones, and so the amount of data that can be gathered is low. Why bother when you probably have a microphone on the same PC that can capture far more sound?

This isn't about audio fidelity, this just about getting audible spoken words, which is definitely possible even with the worst microphone.

I think there was a long period where a proper PC would frequently have only the cheap stereo speakers which are small enough to far outperform raw microphone leads. But I'm not sure this works that well in >=HDMI even if some monitor speakers might otherwise be ideal.