The U.S. stock market's march to all-time highs is putting the spotlight on its large valuation premium over global equities, leading some investors to look abroad for outsize returns. Many investors are reluctant to reduce their U.S. exposure, pointing to better economic and earnings prospects in 2024 for the country over Europe and other regions. The S&P 500's heavy weighting in technology companies also stands to draw investors who want to bet on new fields like artificial intelligence.