Why would mac address only be relevant to IOT devices?

MAC address seems like a useful datapoint to capture on users. This could be used to stitch together users who access a site with snowplow tracking from 2 separate browsers on the same device, correct?
But, in the docs, it’s mentioned that MAC address only makes sense for IOT devices. Why is this so?

@mac-address The MAC address is typically considered a lower-level hardware identifier. While it’s straightforward to access the MAC in an IoT environment, the MAC is not available via any standard browser APIs for privacy and security reasons.