You make the false assumption that people in different divisions of a very large company I'm assuming that people within a company are more likely to know each

You make the false assumption that people in different divisions of a very large company I'm assuming that people within a company are more likely to know each other and know what areas they work on versus simply "working at google." They have all kinds of opportunities to rub shoulders - previous projects they've worked on together, company social events, even just riding the google bus to work each day. While outsiders are also a risk, working for the same company substantially increases the opportunities.