Because there is a clear evidence that this strategy does not work. What you are effectively doing here is creating your own active fund. Even if there is no cost to pay, you are effectively be paying a 1% Forex charges (to buy and sell).
If you are prepared to do the reading, start with CAPM, Fama French 3 factor model to see why this does not work. Have a look at SPIVA report to see how Pros fare (nearly 80% can’t beat the market with access to all the reports and terminals). SPIVA | S&P Dow Jones Indices
If you prefer - watch an excellent series of interviews on the Perfect Portfolio with Nobel prize winners with centuries of investment experience https://www.youtube.com/channel/UCXhZ09ctkeJmJIrZqxJ_zlw/videos - I don’t think I can do better than them.
Beyond the theory, it is also not a strategy that can be put in place for achieving long term financial goals, everyone is an expert in a bull market, can you seriously to do this for 40/50 years? I would rather buy two/three ETFs and sleep well knowing slow compounding will do the job.