The very simple reason Missouri doesn’t observe Daylight Saving Time, along with Arizona, lies in their choice to remain on permanent standard time rather than switching clocks twice a year. Under the Uniform Time Act of 1966, states can exempt themselves from observing Daylight Saving Time by adopting permanent standard time year-round, but they cannot choose to stay on Daylight Saving Time year-round without Congressional approval.
Missouri’s decision reflects this legal option to avoid the biannual clock changes by sticking with standard time permanently, largely for convenience and to avoid the disruptions that come with shifting clocks. Arizona also follows this approach, mainly due to its abundant sunshine—residents prefer earlier sunsets to escape the intense summer heat in the evenings.
So, the simple reason both Missouri and Arizona don’t do Daylight Saving Time is that they have chosen to exempt themselves legally to stay on permanent standard time, a choice allowed by federal law and driven by local preference and practical considerations.
SOURCES
(https://www.senate.mo.gov/25info/bts_web/Bill.aspx?BillID=2724181)(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://www.transportation.gov/regulations/daylight-saving-time)(https://www.senate.mo.gov/25info/bts_web/Bill.aspx?BillID=1331877)
