When I'm mining, I'm gathering resources and then when I'm not mining, I'm usually consuming those resources.
When I'm running a quarry, I'm gathering resources all the time. I saw someone rage at a well known youtuber in their video comment section, accusing them of being a cheater because they had 5 stacks of iron blocks. At that time, I had around 20 stacks of iron blocks. The manual miner's sense of quantity scale is very different from the quarry miner. I also enjoy manual mining but I do it when I want to, never because I have to in order to continue with a project. The manual miner tends to see themselves as 'done' when they've built all of the processing and sorting machines they want. They simply don't generate enough materials to take on projects on much more of a grand scale. When you've got gold chests full of resources and you start thinking about clever ways to use them, the "end-game" opens up rather dramatically.
It's a playstyle thing. You wouldn't know from looking at any part of the overworld on my current map that I've pillaged the mountains under my facilities on a rather vast scale. At the end of the day, letting quarries handle the bulk of my resource gathering frees me to decide what I want to do. If that happens to include some caving or ransacking of abandoned mineshafts, I can do that. I can do all sorts of other things, too, and have the materials to make it happen.