I am looking at Vanguard's Target Retirement Fund VTIVX. This funds' split between US to International stocks is 2:1 (62:27 to be more exact). So for every dollar invested outside US, two dollars are invested within US. I would expect a 1:1 split to be more logical since the US's share of total world stock market is not more than 50% (e.g., reading this link).
Why is the fund biased so heavily towards US?
And this bias is something I have noticed in retirement funds from other provider's also e.g., Blackrock, T. Rowe Price etc.