There is a certain advantage of the BTC price falling while doing DCA, yet falling prices can cause anxiety in regards to some people feeling that they had made their earlier BTC purchases at prices that were too high.
Yes there are some people who regret investing as per DCA. For example if an investor buys Bitcoin at $43k. If he comes to buy bitcoins again according to DCA, he sees that the price of bitcoins has fallen to $40k in the market. Then that investor may regret investing at, $43k. Investors may feel that it is better to invest now rather than earlier.
Again if one buys Bitcoin at $40k while investing in DCA method. If the investor comes to buy Bitcoin later according to the DCA rule, if he sees the price of Bitcoin in the market at $43k. Then again, this investor will think that if he had invested more earlier, he would have earned a lot of profit now. In fact those who invest in the DCA method should have no regrets. Because they are getting an opportunity to buy bitcoins at a higher price and at a lower price. It is human nature to regret whether it is a profit or a loss.