Because there was nothing important or pressing to take care of for the people of Missouri?

United States Constitution:

Article VI
All debts contracted and engagements entered into, before the adoption of this Constitution, shall be as valid against the United States under this Constitution, as under the Confederation.

This Constitution, and the laws of the United States which shall be made in pursuance thereof; and all treaties made, or which shall be made, under the authority of the United States, shall be the supreme law of the land; and the judges in every state shall be bound thereby, anything in the Constitution or laws of any State to the contrary notwithstanding.

The Senators and Representatives before mentioned, and the members of the several state legislatures, and all executive and judicial officers, both of the United States and of the several states, shall be bound by oath or affirmation, to support this Constitution; but no religious test shall ever be required as a qualification to any office or public trust under the United States.

Yesterday, in the Missouri House:

HB 85
Establishes the “Second Amendment Preservation Act,” which creates additional protections to the right to bear arms
Sponsor: Taylor, Jered (139)
Proposed Effective Date: Emergency Clause
LR Number: 0767S.10T
Last Action: 05/14/2021 – Emergency Clause Adopted on Truly Agreed to Bill
Bill String: SS SCS HCS HBs 85 & 310
Next House Hearing: Hearing not scheduled
Calendar: HOUSE BILLS WITH SENATE AMENDMENTS

12/01/2020 Prefiled (H)
1/06/2021 H 54 Read First Time (H)
1/07/2021 H 187 Read Second Time (H)
1/14/2021 H 329 Referred: General Laws(H)
1/26/2021 Public Hearing Completed (H)
1/28/2021 Executive Session Completed (H)
1/28/2021 HCS Voted Do Pass (H)
1/28/2021 H 426 HCS Reported Do Pass (H) – AYES: 10 NOES: 4 PRESENT: 0
1/28/2021 H 426 Referred: Rules – Legislative Oversight(H)
2/01/2021 Executive Session Completed (H)
2/01/2021 Voted Do Pass (H)
2/01/2021 H 451 Reported Do Pass (H) – AYES: 7 NOES: 2 PRESENT: 0
2/03/2021 H 479 Taken Up for Perfection (H)
2/03/2021 H 479 Title of Bill – Agreed To
2/03/2021 H 484 HCS Adopted (H) – AYES: 107 NOES: 43 PRESENT: 1
2/03/2021 H 484 Perfected with Amendments (H) – HA 1, HA 2 ADOPTED
2/03/2021 H 485 Referred: Fiscal Review(H)
2/04/2021 Executive Session Completed (H)
2/04/2021 Voted Do Pass (H)
2/04/2021 H 499 Reported Do Pass (H) – AYES: 5 NOES: 2 PRESENT: 0
2/04/2021 H 499 Taken Up for Third Reading (H)
2/04/2021 H 499 – 500 Third Read and Passed with Amendments (H) – HPA 1 Adopted AYES: 103 NOES: 43 PRESENT: 0
2/08/2021 S 233 Reported to the Senate and First Read (S)
3/11/2021 S 503 Second read and referred: General Laws(S)
3/25/2021 Public Hearing Scheduled (S) – Tuesday, March 30, Noon or uupon morning recess
3/30/2021 Public Hearing Held (S)
4/08/2021 Executive Session Held (S)
4/08/2021 SCS Voted Do Pass (S)
4/26/2021 S 907 SCS Reported Do Pass (S)
4/27/2021 S 985 Referred: Governmental Accountability and Fiscal Oversight(S)
5/05/2021 Public Hearing Scheduled (S) – Thursday, May 6, 8:15 a.m., SCR 1
5/06/2021 Public Hearing Held (S)
5/06/2021 Executive Session Held (S)
5/06/2021 Voted Do Pass (S)
5/06/2021 S 1369 Reported Do Pass (S)
5/07/2021 S 1458 Placed on Informal Calendar
5/13/2021 Taken Up for Third Reading (S)
5/13/2021 Senate Substitute Offered (S)
5/13/2021 Laid Over (S)
5/13/2021 Placed on Informal Calendar
5/13/2021 Taken Up
5/13/2021 SS Adopted (S)
5/13/2021 Third Read and Passed (S)
5/13/2021 Emergency Clause Adopted (S)
5/13/2021 Reported to the House with… (H) – SS
5/13/2021 Referred: Fiscal Review(H)
5/13/2021 Executive Session Completed (H)
5/13/2021 Voted Do Pass (H)
5/14/2021 Reported Do Pass (H) – AYES: 5 NOES: 2 PRESENT: 0
5/14/2021 House Adopts (H) – SS
5/14/2021 Truly Agreed To and Finally Passed
5/14/2021 Emergency Clause Adopted on Truly Agreed to Bill

Quite a rush there.

Yesterday:

Hon. Stacey Newman, Missouri @staceynewman
They truly agreed and finally passed the 2nd Amendment BS Act today & the governor will sign it. Missouri Stop the Steal pro-Constitution GOP has gone mad.
[….]
9:33 PM · May 14, 2021

Gun Sense MO Mom @mizzouatheart
House is now about to consider HB 85, a bill that prohibits and punishes state and local law enforcement from cooperating with federal law enforcement to enforce federal firearms laws in Missouri. This bill is still unconstitutional and bad for public safety. #moleg
4:40 PM · May 14, 2021

Yeah, that pesky “Supremacy Clause” thingy.

Previously:

HB 162: Tenthers and guns, what could go wrong? (January 16, 2013)

HB 2174: Guns, check. Sort of nullification, check. (March 25, 2014)

HB 2196: blah, blah, guns, tenther drivel, blah, recycle, blah, stir… (January 13, 2016)