We don't contribute to FOSS because we are hobbyists or good Samaritans, we do it because we need the features or fixes. We do it because in the long term it is cheaper and more efficient than maintaining a fork or developing a closed source component.
This doesn't mean that the people working in non-web industries "are not playing in the same league" with respect to skill, it just means that they don't have a huge public representation of the work they do.
Sure, but there aren't many people who hate coding but still do it (in significant amounts) in their free time. so having a github profile is still a positive signal towards being a good coder (assuming, of course, that practice causes improvement).
It would be wasteful for a company to ignore this information.
While I understand that many people enjoy writing code and do so for fun, there are a large number of fantastic engineers that don't (myself included). Just as I wouldn't give someone preference for a robust profile, I'm not going to penalize someone for lack thereof. There is only so much time in the day and if they can do ten hours worth of work in eight hours and choose to spend their off time with their family, friends, or hobbies, good for them. Knowing how to decompress and enjoy both work and life is just as valuable to me as crafting solutions to engineering problems.