Because them coming out of a cutscene like I have to find the boss dead or nearly there is a sucky feeling.. here comes this big story fight and oh I missed it because people could not wait 30 seconds..
It's a simple courtesy to make sure you are not ruining someone else's first time experiencing the content. Simple as that. How you can't wrap your head around that idk..
They will never have another first time, does not matter if they will do it again later or never come back. That first time they have ONE shot at.. don't ruin it with your impatience.