Shortcomings of the CAPM include:

Assumptions: The CAPM is based on several simplifying assumptions, such as efficient markets, rational investors, and homogeneous expectations. These assumptions may not hold true in real-world markets, limiting the practical applicability of the model.
Reliance on Beta: The CAPM heavily relies on the estimation of beta, which is subject to estimation error. Estimating beta accurately can be challenging, especially for assets with limited historical data or assets that do not have a close relationship with the market index.
Lack of Consideration for Other Factors: The CAPM considers only systematic risk (beta) in determining the required rate of return. It does not explicitly account for other factors that can influence asset returns, such as firm-specific factors, macroeconomic conditions, or investor sentiment.
Limited Explanation of Cross-Sectional Return Variation: The CAPM focuses on the relationship between an asset’s expected return and its systematic risk. However, it does not fully explain the cross-sectional variation in returns among assets, as it does not consider factors that may drive returns independent of beta.
Market Efficiency Assumption: The CAPM assumes that markets are efficient, meaning that all relevant information is instantly and fully reflected in asset prices. However, in reality, markets may not be perfectly efficient, and investors may have opportunities to exploit market inefficiencies for abnormal returns.