It’s the data write speed. When chasing planets (and to some extent, the Moon), to get the most out of the conditions it’s best to capture at high frame rates, and that requires good and consistent write speed. Not so hard to achieve these days with the price of SSD, but any type of spinning disk will not be fast enough and it’ll drop too many frames.
FWIW, a fast 80mm scope is not what is typically used to chase planets, it’s more of a wide field scope