The CO2 climate forcing does not increase as rapidly as the CO2 amount because of partial saturation of CO2 absorption bands [75]. (journals.plos.org)
Also realise that because the CO2 IR absorption bands near the earth's surface are saturated, the phenomenon of self - absorption means incremental CO2 climate sensitivity is probably slightly negative. (judithcurry.com)
If you carefully study the atmospheric absorption bands you will see that oxygen / ozone does show some absorption in the 14 - 15 um range. (wattsupwiththat.com)