Michelangelo destroyed his sketches and studies so on one would know what went into the preparation of his masterworks, like the Sistine ceiling. He thought it better for the work to feel more miraculous.
The McNeills gave pleasure to the pipe smoking community for 40 back breaking (literally) years. McClelland was their child and they weren't selling their child.
Based on how the world usually works, the chance of a successor company maintaining their sense of commitment was virtually nil, and the McNeills knew that. They like to say it's all about the Virginias, but were seeing a drop in quality that made continuing to do what they did at the level they did it no longer possible. So they weren't going to sell their name and processes to enable an inferior product. Also, making these blends was a highly hands on process, so no Mike McNeill, no blends.
They were offered good money to sell, but it wasn't about the money, rather about the quality and the character, and they had both.