I see where you are coming from but the story is definitely not that complex that 10 writers couldn't complete it in 4-5 years like someone else mentioned. You basically have 2 stories, Ian's and Lena and you write those two mostly separate from one another. You decide where you want to go with them and then write all of the supporting characters depending on how you want them to interact/react with the two protagonists.
Lets use the example of Ian asking Lena for them to be an official couple. The whole idea behind the scene is that Ian asks Lena to be his girlfriend and then you go from there writing the variables. For example, If Lena had sex with Jeremy she will say no to the request, and so on. Maybe writing the dialogue for all of the different scenes is time consuming and hard but figuring out the variables shouldn't be that hard as all of the supporting characters already have a role to fulfill which was assigned to them.
Of course its not in the point where 10 writers cant complete it even after 4-5 years, and i agree with you... but its also not as easy as you said, even if you already plan everything like side character and their roles in the game, its still hard to makes good story for it, its always easy to figure it out the outline of the story, but to makes the dialogue and the narrative for it is the hardest part, if you dont believe me, try it yourself and write any kind of novel, its always easy to figure it out the outline and at start its easy, but after around 100 chapter, you will see that the difficulty will gone up, you need to makes chapter 101 base on 100 chapter before that you already made, if you made a mistakes in the previous 100, you can easily encounter writer block, cuz i experienced it myself, even though i only write my novel for fun and when i got bored with all that programming stuff at college, but i still plan to release my novel on novel platform like webnovel in the future...
I always create the outline for every chapter first and plan it as good as i can before writing it, and my friends that has popular novel in different platforms also do that so they can create the novel more easily, but its still hard for us, cuz outline its nothing if we compared it to the story in every chapter even if we plan everything in the start, i can come up with the outline for 100-150 even 200 chapter ahead in matters of few days and its easy, but writing it? it takes a month if im fast, or few months if i got writers block, chapter 1-100 its always easy for me and my friends, but after that its became tricky, how you write the story as good as you can, how the writing makes the reader felt interested and how to makes the dialogue felt natural without any cringey line that doesnt even sounds natural and you need to take a note on everything that happend in previous 100 chapter so that the new story still had correlations with previous chapter...
For me who doesnt publish my novel on any platform its rather easy to fix writer blocks problem, i just revised the chapter that blocking the idea that i wanna uses in new chapter so that idea can be used in new chapter. But for my friend that already published their novel in different platform, they cant do that, and they need to used the story that already published as good as they can, thats why they faced more writer blocked than i am.
Even for author of novel that has a multiple popular novel in different platform (not like 100k, but 2-5 million views for each novel) its still very hard to come up with new and good story, so i cant agree with you for millions years that said writing its not that hard, but the reality is, IT IS very hard, try it yourself if you dont believe me
