I know several people personally that did. Among people who have worked in the cryptocurrency industry it's not unusual that they've cashed out small portions of their stash in each bubble but still hold some today.
Yeah, this is the “safe” way to do speculative investing: when the asset price goes up, at one point or another you can take out your original investment, and the rest becomes “pure profit”. At that point the worst case scenario is that you break even.
I agree, I would not have either. But my present financial philosophy for such things is to always sell half (and only half).