Because the problem is beyond just 'slightly longer queue times'
It's about queue health in general.
Say some guy is a mid main/secondary support, so they queue mid/support.
Without autofill, they get support 90% of the time, and get mid 10% of the time.
So they say fk that, and start queuing mid/top, then just ask for a trade/or dodge if they land top.
Ok there's one less person to fill in support role.
Now queue times get slightly worse.
Now the next guy who is a mid 1st/support 2nd main gets support 91% of the time and mid 9% of the time. Cause, eventually, someone's gotta be that support.
This falls completely downhill till you put support or fill as any of your pref, you're 100% guaranteed to get support.
Which leads to less and less people queuing either role as support or fill, except your diehard support mains. Which it's already known that they're vastly under-popular.
So now queue times start rising on their own, because the system is just having 4 guys sitting in queue waiting for 1 to be willing to play support.
Now you have longer queue times than before, and don't even have autofill to fix it.
Then their algorithm just has to break down and start pulling every single person who queues support into a game ASAP, regardless of mmr differences.
Now we have decent queue times again, but vastly unfair matches being decided purely on which side pulled the higher ranking support main.
And this would just get worse and worse as time goes on because each 'fix' that is not autofill, is just a band-aid fix that will delay the problem of low queue times vs getting roll you queued for.
So, no, it's not just 'I'm ok waiting 3 extra minutes to get the role I want.'
Because, while this week, that might be true. Next week it might be 4 or 5 extra minutes. Then 6 or 7 the week after that.
Because it just comes down to: If <1/5th of League players do not want to play support, eventually, someone who does not want to play support will have to be forced to play support.
It's just basic math.
And if you want to go back to old draft system, (without pref roles)
It will 100% degrade back to people spamming 'mid or feed'
Because that's just human nature. When we want something, and we don't get it, we get angry.
And without some form or hard laws or 'mothering' there to prevent it, we'll take it even when we know we're not supposed to.