What is the cause of the valuation differences between the US and the rest of the world?

Valuation for US stocks are higher than the rest of the world. What is the cause? Vanguard does a good job of visually providing a breakdown for the last ten years. Clearly, a clear driver is valuation from investors, but what is very clear is the strong impact of revenue growth. Revenue has been much stronger in the US than the rest of the world. What is surprising is the relatively small impact of profit margin expansion versus what is seen in the ACWI ex-USA. US companies have grown the top-line and have been rewarded with higher valuations even though margins have not expanded. The big gains in the US equity index are all driven by the huge gains in revenue and valuations within the information technology sector. Overall, the US and global differences could mean that US companies are more sensitive to any changes economic growth or investor sentiment related to valuations.