Good managers in my experience have three important jobs: Scoping projects and getting the team together, motivating employees and handling their compant interfacing problems (talking to HR for them, managing account access issues, ect.), and most importantly talking with clients/stakeholders in a sympathetic ans professional way that many developers just won't do at the same quality. All of that might only take 3 hours of video calls per day, but for the good ones, it's a full day's work. For some, certain functions they're doing aren't needed, but most of the managers I've had have done valuable work that I wouldn't do as well and wouldn't want to have to do which would distract me from my work.
Could professional football teams likely also have the players figure out training schedules, plane flights, diets, plays, recruiting? Probably, and some might be pretty good at it. So why don't they? Probably the reason those teams have coaches is the same as why managers in the tech space aren't all going to be proven useless working remotely, because they actually aren't.