Why is Halo so difficult to make?

All of the Halos, every single one of them, has great problemas in their production… the saga is cursed? Bungie, 343i and Assemble Studios (RIP) had problems, like crunch, no time, many bugs, tooo many idead in the trash. Maybe you are gonna tell me this happens in every videogame developer, and you are right, but literally in this saga the problem is multiplied by 5, all the time, with this 3 companies the employees get so exausted in the working of Halo games.
For you guys, why is so difficult to make?