Why? Knowing the fact that the next bull price will still come as bitcoin continues to grow, so I don't think selling all my bitcoin in the bull market is the best.
You can always buy back later for the next bull run. And looking at the past performance, the price difference between bull market and bear market is quite big, so in the past selling all coins wasn't a risky decision if you sell late during the bull run. The biggest risk in selling all coins is that the price will keep going up and never fall down below that level ever again. To avoid this it's better to not sell early in the bull market and wait for the bull market to mature.