Why isn't it meta for adcs to start with sweeper?

It isn't really a good idea for anyone to start with sweeper. Very early game (think before first back), it is more important to have vision and just know where the enemy does as well then to actively deny the enemy, which is why everyone starts off with totem, to get those lane safety wards out. As for why they don't take it afterward? Probably because for an ADC, it is more effective to have either the upgraded totem (to help ward the map) or the farsight, to keep view of an enemy as they fight.