i don't understand why we have qualifiers for LAN events when players can just simply say no if they win, or take forfeit wins / wins against players who would actually attend early on in the tournament when they 100% won't go themselves anyway.

Here's a theoretical situation:

You lose 2-1 to the winner of the tournament on the left side of the bracket, he turns down the invite - the 2nd place player on the right side of the tournament loses 2-0 in the final, however he now gets the place even though his loss was heavier than the first player who lost earlier on in the tournament, even if the left side player is better it doesn't matter, but then this 2nd place player also decides not to go but doesn't confirm that until the last minute... perhaps he was never intending to go anyway but just wanted to play in the tournament to ruin it for other people? So then some random guy at the tournament who didn't even take part in the qualifier plays instead, because he took a gamble.

I've seen it happen several times, and it's absolutely stupid.

TLDR version:
We need a better format to run these tournaments that won't allow people who will 100% not attend, play in them. Else just give direct NON-BYOC invites to some players, and then allow anyone else to turn up and play on the BYOC if they want too.