It is better to target at several prices and not sell all your coins at once because we can get profit if the price goes higher than $100K, many do that. I also do it sometimes and get higher profit if the price goes up again.
I also sell my altcoins at several price targets, not just at one price.
Selling everything once is never a good idea - there are times when you go all out and sell off all your holdings because you feel that price was good but after sometime (while you’re still waiting for the price to drop so that you can buy back to hold) you noticed that the price keeps increasing.
The last all time high that bitcoin got to, a lot of people sold before hit got to that price because they felt it won’t increase more than that while some sold part of their holding and when it got to all time high they sold some part of it too, and when it reduced they used the money to purchase more bitcoin and are currently waiting for the price to drop so they can buy more.
Selling, especially at a very high price can be very profitable if only the seller probably had a second chance of buying at a lower rate again. But is it worth the risk at all?. Bitcoin price movement is uncertain. Selling at a good price, with the mindset of buying at a lower rate is a tough risk on its own, because we might sometimes be compelled to wait for a very long time before getting a lower price that suits our purchasing power. So I agree with you that selling all holdings at once is never a great idea.
Just imagine someone selling his/her holdings when Bitcoin was around $70K some months back, and had to wait till when Bitcoin touched down to $53.8K(which happened sometime last week). The timeframe to experience such dip is so lengthy and d I don't think everyone will be willing to take that risk, though there are some investors that are natural risk takers, and can even go beyond that.