Mostly it's because having good ventilation makes it pretty much moot.Are people just saying "it's not needed, they are fine." OR are people saying there is something BAD/WRONG about it?
Also because rodents/insects can make home in it or in between layers of insulation and interior and/or exterior wall sheathing.
..and if it's not protected from the birds having access they will eat it.
If you want to use it, great, but there are valid reasons.