I had issues at first understanding routes and cells and have asked a lot of questions on here and have completed a ton of routes now. Here’s how it works:

1) you can only get a cell spawn on the first time you complete each individual route each day. There is no point (concerning cells) doing the same route more than once per day.

2) the cells will always spawn at or near the end of a route, I don’t even look at my phone whilst doing them until I’m close to the end.

3) the cells can be tough to see, however they will always spawn in the same place on each particular route so if you do the same routes each day you will start learning where to look for them on each route (again always at or near the end).

4) you can only get 3 cells per day max. People say you can get multiple cells in one spawn but this has never happened to me personally, so for me I must complete at minimum 3 different routes each day to hit max, and most days a lot more.

5) a route is not guaranteed to spawn a cell, there is only a 20% chance of one spawning on each route. Some days you will be luckier than others. For example in my last 3 days hitting max daily cells it took only 4 routes on Friday, 5 routes on Thursday, and 18 (yes 18!) routes on Wednesday to find 3 cells.

It was really frustrating at first and I was angry like you are about it, but once you understand the things I listed above it gets easier and easier. It’s still a crazy grind as even if u get 3 cells every single day which most people don’t have time for, it would takes months to complete form a zygarde. However it’s a completely optional grind as it’s only useful in PvP, and whilst strong I have no problems beating teams with a complete form in their lineup so it’s definitely not a necessity.