Originally Posted by keitherson

Because no one calls it Y+

They call it W

Y+ is exactly Y+: economy with + space

Economy Plus(UA)
Main Cabin Extra (AA)

Presumably Delta doesn't call it Main Cabin Plus is because they also provide free drinks, snacks, that other carriers do not. On UA and AA it's literally just extra legroom. Not even Priority Boarding.

That's also why AS calls it Premium Class.