Why does autofill exist in normal draft ?

I never got the point of it tbh. Most of people who play there do it to learn certain specific role or a champion or try diffirent builds , so they try to prepare themselves for upcoming ranked games and there are those like me who are preparing for next season climbing , because in normal blinds they can barely get their role so that they go in a queue to choose their roles that they want to practice , then the autofill is a slap in the face that just forces them to play something else entirely , and saying that autofill 95% of the times is the support , and if you say ask politely for a role trade you BARELY find anyone who wants to trade with support , especially at where i am at , gold division. Basically it is like that : You either play a role you don't want to play or receive a punishement. I don't mind longer queues , i just wanna play my roles that i want to git gud at stop forcing me to play something i don't want , in normal games.