DHH, the creator of Ruby on rails, once said that they mostly hire people based of their GitHub commit to the Ruby or rails projects.
It helps him to understand the candidate's level of commitment, coding practices and many other things needed to work in his company.
I guess that's the main reason.
To understand the mindset of a candidate, it's not how often they push .
But how well they code and how well they mingle with the team and follow best practices.
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