1 reason to sell could be if someone only had so m

1 reason to sell could be if someone only had so many shares and wanted to stay under a specific tax rate. Sell some this year for a low rate and then sell more next year. The tax tables are not kind for a large sum of money earned in the market in the short term. Also on long term once you get over a certain amount you get hit with an extra 3.8%

These conversations are what tax consultants are made for.