One of the important roles of the National Committee on Uniform Traffic Control Devices (NCUTCD) and its members is to ask hard questions about proposed devices and treatments. Is the sign, marking, signal, channelizer, or other device effective in its intended role? It it well understood by road users? Does it send unintended messages? Is it only effective or useful under limited conditions? Does it reduce one type of crash while raising the risks of other crashes? Those are just a few questions that might be raised - and members are encouraged to raise them. And these members are typically experienced practitioners, subject matter experts, or others who have learned what questions to ask. Although NCUTCD doesn't "own" the MUTCD (it's published by USDOT), the committee does try to provide good advice to USDOT / FHWA on nearly all of its content.
Activists and advocates frequently decry or dismiss NCUTCD's process and pace, saying it's "obsolete" or "inefficient". And sometimes devices are included or fast-tracked in the national manual "at the direction of the Secretary". But I think this deliberative and thorough process is important, as the end result is a US national standard that can exist for many decades, so it's advisable to give it a lot of scrutiny at the draft level instead of trying to amend it later.
See
https://ncutcd.org/aboutus/ for more info on NCUTCD.
Repeating my disclosure: I served as the chair of the NCUTCD Bicycle Technical Committee from 2002-2017, and am currently under contract to run the day to day operations of the organization.