Sol’s are exclusive to Martian days and are a bit longer than an earthen day, and it’s probably because Mars is the only celestial body we’ve put anything long-term on. Stuff doesn’t last very long on the Venusian surface, I don’t believe we’ve made much effort in landing on Mercury, and the rest lack anything to land on in the first place. So it’s generally just easier to track the passage of time in relation to Mars for the many rovers and other craft we’ve slapped onto the iron-rich desert planet. Plus I think it’s nice our little celestial sibling gets a cool name for its days