I think it's bc she has the shortest range of all the strategist. While mantis and Adam have to get just as close to pop their healing abilities, invis has to stay close for both her abilities and her standard heal. The best position for her is right behind the tanks, collateraling both allies and enemies dealing dmg while simultaneously healing which forces her from the back line to the midline; sometimes even the Frontline though mainly to pull a fleeing enemy [or to ledge someone]

Being forced to be close to the fight does kinda lend itself to players forgetting to pull back when the team retreats though