On one hand, i understand that they prefer to pick champions that are statistically better than others.
I also understand that you can only have so many champions that you can master, so a smaller champion pool is easier to maintain.
On the other hand, it's been provrn multitudes of time that off-meta picks can be just as viable. Hence why you can see almost every champs played in Master/Challenger, despite being criticized as ''subpar''
Worlds players are essentially a bunch of challengers... there's little reason that could explain why off-meta wouldn't work for them.
But yeah, i stopped watching worlds because i was sick of seeing the same champs over and over and over again. I'll be back in the finals.