1st: it wasnt nerfed yet when teams were picking them and when it got nerfed and fade came out, sova's usage rate plummeted.
2nd: in addition to the abysmal pickrate, he also have an abysmal winrate on bind(you can check the stats if you want), especially against teams that weren't picking sova. Sova dart gets like barely any value on bind because u hall, showers, and hooka exists, his drone clears barely any and there is so many better replacements (Skye dog, fade cat, boombot). His ult and shock dart is decent but I don't think that is the reason anyone pick sova.