Why Vanguard does not offer a single ETF that replicates the classic three-fund portfolio (U.S. stocks, international stocks, and bonds)?

It could come in 20/80, 40/60, 60/40, and 80/20 options. In my opinion, such ETFs would become instant best-sellers in the market. They could have quarterly or semi-annual rebalancing, providing a one-stop option so investors can optimize their portfolios with ultimate simplicity.

In Canada, Vanguard offers something similar but with higher fees (0.24%). Why not in the US market?