Do you mean zooming out a 16x9 image to have the same width as your 2.35:1 screen and cut off the top and bottom? The obvious reason is you cut off the top and bottom of an image, which is even more intrusive then cutting the sides off a cinimascope image. Another reason is often shows I watch in 16x9 are sports or TV shows that may not be from the best source (maybe YTTV or ESPN+) and having them at 150" from 11' viewing distance doesn't help a poor source. Of course I watch other 16x9 content that does look pretty good like Jack Ryan which is 4K UHD or the Game of Thrones Blu-Rays.
Instead I use lens memory to zoom 16x9 content to the same height as my 2.35:1 screen. I believe that gives me a 114" image on my 142" scope screen.
7.4.4 Theater Room: JVC-RS500, Silver Ticket AT 2.35:1 142”, Onkyo RZ830, Anthem PVA-7, Panasonic UB420, Apple TV 4K, JBL Studio 530’s, Dual Driver VBSS
3.1 Living Room: Samsung 64” F8500 Plasma, Anthem MRX 300, Dynaudio Audience 52’s, Dynaudio Audience 122C, NHT SubOne, Roku Express (2019)