A pattern emerges

The Fourth Schedule to the Constitution is an interesting thing. The national government, in Part 1, is responsible for,

22. The protection of the environment and natural resources with a view to establishing a durable and sustainable system of development, in particular--
(a) fishing, hunting and gathering;
(b) protection of animals and wildlife;
(c) water protection, securing sufficient residual water, hydraulic engineering and the safety of dams; and
(d) energy policy,

while county governments, in Part 2, are responsible for,

2. County health services, including, in particular--
...
(g) refuse removal, refuse dumps and solid waste disposal.
3. Control of air pollution, noise pollution, other public nuisances and outdoor advertising.
...
10. Implementation of specific national government policies on natural resources and environmental conservation, including--
(a) soil and water conservation; and
(b) forestry.

In relation to the ban on plastic bags by the Cabinet Secretary for Environment and Natural Resources, the National Environment Management Authority has published an infographic that states, in response to the frequently asked question, "What are the major concerns of plastic bags?"

Plastic bags are usually manufactured for single use and generally tear or puncture after a first use. They are easily transported  by the wind and are some of the most visible components of roadside and shoreline litter. Plastic bags are produced from oil and natural gas, and never fully biodegrade, remaining in the environment as small or even microscopic particles, essentially forever.

"Roadside and shoreline litter" are "solid waste", the disposal of which is the responsibility of the county governments. The Fourth Schedule, in relation to the responsibilities of the national government vis-a-vis soil and water conservation -- which may be affected by the non-biodegradability of plastics -- is limited to the making of specific policies whose implementation is left to the county governments. (I am aware that "policy" may include legislation like the Cabinet Secretary's "ban" but the enforcement of that legislation is solely the responsibility of county governments.)

@Keguro_ wonders what NEMA's and the Ministry's legal departments do with their lawyers. It is a question that I fear may never be answered in full. It should have been obvious from a reading of the Fourth Schedule that the Cabinet Secretary's purported ban does not pass constitutional muster. This is in addition to its other glaring infirmities when seen in the light of the Cabinet Secretary's powers under section 86 of the Environmental Management and Co-ordination Act, 1999.

@Olez observes that there is no (presumably, national) concrete solid waste management plan, but that is not strictly accurate, is it? Solid waste management has always been the preserve of local authorities and their successors, county governments. What those plans have been is poor. Part of the reason they have been poor plans is that the participation of the people in their formulation, implementation or enforcement has been inadequate, to say the least. As a result, county governments, and their licensees, simply collect solid waste and dump it in designated (and, frequently, undesignated) zones. In these places, human scavengers, at great risk to their safety and health, sort the sold waste into different categories, plastics included, and sell them on to waste-recyclers and other manufacturers. In the absence of a national solid waste management plan on paper, this is the management system in place at the county level, a system that the Ministry is mulishly and deliberately ignorant of.

There is little different between the Cabinet Secretary and the chief executive of the Kenya Film Classification Board or the executive director of the NGO Co-ordination Board: all three have attempted to exercise administrative powers that don't exist in law, are attempting to enforce laws that do not exist and do both with the threat of draconian fines and other penalties. One is a mistake, two is a coincidence, but three is a pattern. We did not stop the KFCB head honcho because we laughed at his buffoonery. We have so far failed to stop the NGO Co-ordination Board because he is "protected from on high". Now it is almost certain that the Cabinet Secretary will get her way with this farce of a ban.