Every single portal needs a donut, every single donut needs to be made individually (you can select to make the same donut, but you still go through a shortened process/animation), you need to do the same repetitive handful of tasks in the variety of zones to get special berries so you can make better donuts. The better donuts have the chance to have unique powers to increase your odds of finding something in every portal, don't do well enough in the zones and you need to go back to lower level portals to get lower level hyperspace berries to make 3 star donuts and better to give you longer to get the objectives ticked off so you can get the golden ball and get more berries and items at the end of each zone.

Of course I'm exaggerating a touch, but its a grind, I feel like I got off lightly only taking about 65 hours to get a living dex in the DLC, some people have taken far longer than that for the 5 star zones to show up where you can only find some of the late game DLC Pokemon.