The very simple reason why Missouri doesn’t do permanent daylight saving time, along with Arizona, is because under the federal Uniform Time Act, states may exempt themselves from daylight saving time only by observing permanent standard time year-round, not by staying on daylight saving time permanently.
Missouri currently follows the biannual clock changes but lawmakers have introduced bills aiming to exempt the state from DST and adopt permanent standard time, or switch to permanent daylight saving time only if the federal government officially makes DST year-round the national standard—which requires congressional approval.
Simply put, Missouri, like Arizona and Hawaii, could opt out of DST only by sticking permanently to standard time rather than staying on daylight saving time permanently, unless the federal law changes. This explains Missouri’s current stance and legislative efforts to “lock the clocks” in place without shifting twice a year.
Sources
(https://www.yahoo.com/news/where-missouri-lawmakers-stand-ending-005556122.html)
(https://thehill.com/homenews/nexstar_media_wire/4522217-daylight-saving-time-these-2-states-didnt-spring-forward-this-morning-heres-why/)
(https://en.wikipedia.org/wiki/Daylight_saving_time_in_the_United_States)
(https://thehill.com/homenews/state-watch/5464355-daylight-saving-time-which-states-want-to-stop-changing-the-clocks/)
(https://www.ncsl.org/transportation/daylight-saving-time-state-legislation)
