Different people have different strategies in terms of investment and everybody have a particular strategy that work for them.
Buying Bitcoin by DCA does not necessary mean that the investor have limited capital, most people that buy Bitcoin by DCA still have the capital for lump sum but one of the reason why some people prefer DCA to lump sum is that some people see lump sum as a method that is risky because of the volatile nature of Bitcoin which they cannot possible tell what the price may be in the future. So to avoid any uncertainty in regard to dip they see DCA as precautionary way of buying Bitcoin than lump sum which requires buying Bitcoin at once with the capital at hand without considering whether the price will dip or not.
The truth is that if an investor see's lump very risky because of the volatility of bitcoin I don't think the DCA method of investing will be seen in a different way because these are different strategies of investing but the same market. I do not agree with you why you think people don't prefer lump strategies because of the volatility of bitcoin, even in the DCA method volatility still happens. People just prefer to use DCA because it is straightforward and stress free. The most important aspect using the DCA method to invest is that you can be very consistent with your investment because you are just investing with amount you can afford, it doesn't matter what the amount is but the important thing is that one is investing with ease.