Presumably, to remove the automation, they also removed the reasons WHY workers were such an automatable thing in the past. I think those reasons were:
1) Lots of things for workers to do - every single tile in the radius of the cities (if the cities were tall)
2) After the first few things (luxuries, resources) the order only matters a bit.
3) There's no tradeoff to improving tiles - the workers are there, they might as well do something useful, there's rarely a reason to hold off.
4) Workers work slowly, so by the time one of them finishes an improvement you've probably forgotten what else you want it to do, you have to re-assess and think about something that isn't important anyway.
Combined, all those things together made worker management boring - lots of things to do, but very few of the decisions particularly interesting or impactful, if your workers just stay busy doing whatever for the whole game your cities just get better.
In Civ 6, they've tried to address these in a few ways.
Since districts and wonders are now built on the map, there's no longer a point to improving every single tile around. In fact, with adjacency bonuses, removing or changing terrain may be counterproductive, and perhaps there's no point in improving a tile you're going to place a district on later. In addition, improvements are no longer free, since builders have limited charges and need to be rebuilt. You won't have a swarm of builders around and be forced to decide what to do with them just because they're there. Since building improvements is instantaneous, you won't be in a situation where a builder becomes active and you have to re-think "man, what is useful for this guy to do around here? What's going on?" because a builder is only going to be around for a few turns total.
The designers believe that those changes are enough to make decisions of what to do with your builders interesting and meaningful, rather than a chore. You'll only build a builder when you have something in mind for it to do, it will only be there for a few turns so you won't have to keep figuring out over and over what you want from it, and the choices of where to improve are more interesting then before, due to the interactions with districts and the limited charges.
We'll see how well it works when it comes out, obviously. But I can certainly see the idea.