Even though I know what you said is true, most investors with small capital can't afford that. Their fund is too low so they want to squeeze out every possible juice they can get to increase their profit margin. Or even try to DCA only when it comes close to the bottom as much as they can. So it always has that kind of investor who tries to spot the bottom no matter what.
How can they detect the price is close to the bottom when they don't know what the bottom is. No one can tell that the last price is the bottom because no one really knows, they can only guess. Anyway, even with small capital, investors can DCA by buying a little every dip or lower lows. We don't need to buy a whole or a half of BTC just to DCA, we can buy thousands of satoshi and accumulate from there.