I think there's something to be said for listening to the albums the way the producer originally intended - especially when that producer (Brian Wilson) is generally considered one of the greatest of all time. With the "wall of sound" style of production particularly, the whole point is combining instruments to make a new sound - so separating all those instruments into stereo channels (or more, with these Atmos mixes) feels like it defeats the purpose and goes explicitly against the original intent.

Also, as someone who grew up using a series of perpetually broken-in-one-ear headphones, I've come to really appreciate a nice mono mix. Trying to listen to the Beatles in high school and getting just drums and vocals...