Earlier quoted context omitted.
The point is more or less, if VC invests (or plans to) in 20 software companies, investing additionally in something like GitHub or npm makes it more likely that the other 20 companies will succeed. They don't invest just in GitHub from the goodness of their hearts.
To add, if Github goes into a death spiral they'll likely take a few of those 20 companies with them. In the same way if AWS goes down, so does half the Valley.
Is that a skewed view? Are there many big companies that would disappear without being able to move to a different platform in under 2 weeks?