>>715124167
I have no idea who you're talking about, and I don't think I want to know.
It's simple, really. Some of the big mod lists have over 3,000 mods, with a lot of worldspace edits and extensive balancing to get spells to scale properly and leveled lists to work with all the monsters. If you just download all the mods yourself, you're going to run into conflicts and bugs. Without edits and patches, you'll get crashes or massive FPS drops. You can't scale to that level without fixing and optimizing the game.
Granted, a lot of these mods are filler, since they cover playstyles you might never use. But even a super-focused mod list with 300+ mods can run really well. I suspect most custom Skyrims could be much better if people optimized them with patches, bug fixes, and similar improvements.
You just think about what kind of Skyrim you want to play, see if there's a mod list that's similar and has already done a lot of the work, then modify that list to make it exactly what you want. This approach is especially helpful if you're new, since you can adjust things over time. You don't need to know all the best or most optimized mods to make the game functional at different levels, and if you're an expert, it just saves you time.
Doing it all yourself in a high-quality way is a massive effort. Just look at the bugfix sections of some of the bigger mod lists. It's pretty crazy how many hours it takes to cover everything. Why reinvent the wheel if you just want to play, unless you're trying to create something truly new and want to share a different way to experience the game?
